1 As of July 2005, there were over fifty thousand in the UN database. See United Nations Treaty Collection, Overview, available at <http://untreaty.un.org/English/overview.asp>.

2 See, e.g., Aust, Anthony, The Theory and Practice of Informal International Instruments , 35 Int’l & Comp. L.Q. 787 (1986)CrossRefGoogle Scholar; Hillgenberg, Hartmut, A Fresh Look at Soft Law , 10 Eur. J. Int’l L. 499 (1999)CrossRefGoogle Scholar.

3 An early exemplar of this approach is Richard B. Bilder, Managing the Risks of International Agreement (1981).

4 e.g., Commitment and Compliance: The Role of Non-Binding Norms in the International Legal System (Dinah Shelton ed., 2000) [hereinafter Non-Binding Norms]; Ho, Daniel E., Compliance and International Soft Law: Why Do Countries Implement the Basle Accord? 5 J. Int’l Econ. L. 647 (2002)CrossRefGoogle Scholar.

5 The same can be said about compliance generally. See Raustiala, Kal & Anne-Marie, Slaughter, International Law, and International Relations, and Compliance, in Handbook of International Relations 538 (Carlsnaes, Walter et al. eds., 2002)CrossRefGoogle Scholar.

6 e.g., Jutta, Brunnée & Toope, Stephen J., International Law and Constructivism: Elements of an Interactional Theory of International Law , 39 Colum. J. Transnat’l L. 19, 65 (2000)Google Scholar (“[L]aw’s existence is best measured by the influence it exerts.”).

7 This question tracks one that is sporadically investigated in contract law: Why do parties opt out of the legal system? For example, “[t]he diamond industry has systematically rejected state-created law. In its place, . . . the industry [has] developed an elaborate, internal set of rules, complete with distinctive institutions and sanctions . . . ” Bernstein, Lisa, Opting Out of the Legal System: Extralegal Contractual Relations in the Diamond Industry , 21 J. Legal Stud. 115, 115 (1992)CrossRefGoogle Scholar. However, as Herbert Bernstein and Joachim Zekoll argue, “It is extremely difficult to determine, with any degree of certainty, how widespread the use of permanent ‘no-law’ agreements is in actual American business practice . . . . [N]o such agreement will ever surface in a court of law unless the parties differ as to its effect.” Bernstein, Herbert & Zekoll, Joachim, The Gentleman’s Agreement in Legal Theory and in Modern Practice: United States , 46 Am. J. Comp. L. Supp. 87, 88 (1998)Google Scholar.

8 They are also a central feature of transgovernmental networks, an increasingly important mode of cooperation. See generally Anne-Marie, Slaughter, A New World Order (2004)Google Scholar (arguing that governments are increasingly working together through transnational networks, on issues ranging from trade to terrorism, to respond to the challenge of interdependence); Raustiala, Kal, The Architecture of International Cooperation: Transgovernmental Networks and the Future of International Law , 43 Va. J. Int’l L. 1 (2002)Google Scholar.

9 E.g., Schachter, Oscar, The Twilight Existence of Nonbinding International Agreements , 71 AJIL 296, 304 (1977)Google Scholar (“[N]onbinding agreements may be attainable when binding treaties are not...”). Schachter “was one of the first promoters of the concept of’soft law’ alternatives to rigid treaty and custom, and perhaps the first to note the potential legal import of’quasi-legal agreements’ and General Assembly resolutions.” José E., Alvarez, In Memoriam: Commemorating Oscar Schachter, the Teacher , 104 Colum. L. Rev. 556, 558 (2004)Google Scholar.

10 Some of these dimensions have been examined elsewhere. See, e.g., Barrett, Scott, Environment and Statecraft: The Strategy of Environmental Treaty-Making (2003)CrossRefGoogle Scholar; Koremenos, Barbara et al., The Rational Design of International Institutions , 55 Int’l Org. 761 (2001)CrossRefGoogle Scholar. Precision of obligations might arguably merit inclusion as a criterion. I do not focus on precision for reasons discussed below: as the rules-standards literature illustrates, rule precision is not per se advantageous and the significance of precision is closely linked to the structure of review, in particular when institutions are tasked with elaborating standards ex post.

11 See, e.g., Lipson, Charles, Why Are Some International Agreements Informal? 45 Int’l Org. 495 (1991)CrossRefGoogle Scholar.

12 See, e.g., Aust, Anthony, Modern Treaty Law and Practice 26 (2000)Google Scholar.

13 See Hillgenberg, supra note 2, at 500; Schachter, supra note 9, at 299.

14 Baxter, R. R., International Law in “Her Infinite Variety,” 29 Int’l & Comp. L.Q. 549 (1980)CrossRefGoogle Scholar.

15 Vienna Convention on the Law of Treaties, opened for signature May 23, 1969, Art. 2, para. 1(a), 1155 UNTS 331 (entered into force Jan. 27, 1970).

16 South Pacific Nuclear Free Zone Treaty (Treaty of Rarotonga), Aug. 6, 1985, 24 ILM 1440 (1985).

17 Convention on the Rights of the Child, Nov. 20, 1989, 1577 UNTS 3 (entered into force Sept. 2, 1990).

18 UNIDROIT Convention on Stolen or Illegally Exported Cultural Objects, June 24, 1995, 34 ILM 1322 (1995), available at <http://www.unidroit.org/>.

19 Stockholm Convention on Persistent Organic Pollutants, May 22, 2001, 40 ILM 532 (2001), available at <http://www.pops.int>.

20 Conference on Security and Co-operation in Europe: Final Act, Aug. 1, 1975, 73 Dep’t St. Bull. 323 (1975), 14 ILM 1292 (1975) [hereinafter Helsinki Final Act].

21 Announcement of the Ministers of Finance and Central Bank Governors of France, Germany, Japan, the United Kingdom, and the United States, Sept. 22, 1985. 24 ILM 1731 (1985), available at <http://www.g8.utoronto.ca/finance/fm850922.htm> [hereinafter Plaza Accord].

22 The International Convergence of Capital Measurement and Capital Standards (Basel Accord), July 1988, and its amendments are available on the Web site of the Bank for International Settlements, at <http://www.bis. org/publ/bcbs04a.htm>. In January 1999, a new capital accord was proposed by the Basel Committee that came to be known as Basel II. International Convergence of Capital Measurement and Capital Standards: A Revised Framework, June 2004, available at <http://www.bis.org/publ/bcbsca.htm>.

23 Non-Legally Binding Authoritative Statement of Principles for a Global Consensus on the Management, Conservation and Sustainable Development of All Types of Forests, Aug. 14, 1992, 3 Report of the United Nations Conference on Environment and Development, UN Doc. A/CONF. 151/26, Annex 111(1992) [hereinafter Forest Principles Statement], available at <http://www.un.org/documents/ga/confl51/aconfl5126-3annex3.htm>.

24 Founding Act on Mutual Relations, Cooperation and Security, May 27, 1997, NATO-Russ., 36 ILM 1006 (1997), available at <http://www.nato.int/docu/basictxt/fhdact-a.htm>.

25 See Paris Club Press Release, The Paris Club and the Republic of Iraq Agree on Debt Relief (Nov. 21, 2004), available at <http://www.clubdeparis.org/rep_upload/PrIraq21 nov04.pdf>; see also SC Res. 1483 (May 22, 2003), 42 ILM 1016 (2003).

26 e.g., Aust, supra note 2; Boyle, Alan E., Some Reflections on the Relationship of Treaties and Soft Law , 48 Int’l & Comp. L.Q. 901 (1999)CrossRefGoogle Scholar; Goldsmith, Jack L. & Posner, Eric A., International Agreements: A Rational Choke Approach , 44 Va. J. Int’l L. 113 (2003)Google Scholar; Helfer, Laurence R., Regime Shifting: The TRIPS Agreement and New Dynamics of International Intellectual Property Lawmaking , 29 Yale J. Int’l L. 1 (2004)Google Scholar; Hillgenberg, supra note 2; Edith, Brown Weiss, Introduction to International Compliance with Nonbinding Accords 1 (Edith, Brown Weiss ed., 1997)Google Scholar; Mathews, Jessica T., Power Shift , Foreign Aff., Jan./Feb. 1997, at 50 CrossRefGoogle Scholar.

27 Though nonlegally binding, pledges are often connected to the development of customary law. Pledges “sometimes have provided the necessary statement of legal obligation (opinio juris) to evidence the emergent custom and have assisted to establish the content of the norm.” Shelton, Dinah, Introduction: Law, Non-Law and the Problem of ‘Soft Law,’ in Non-Binding Norms, supra note 4, at 1 Google Scholar.

28 Kahler, Miles, Conclusion: The Causes and Consequences of Legalization , 54 Int’l Org. 661, 661-83 (2000)CrossRefGoogle Scholar; Simmons, Beth A., The Legalization of International Monetary Affairs , 54 Int’l Org. 573 (2000)CrossRefGoogle Scholar. Simmons argues that “[international monetary legalization can be characterized by an inverted ‘J’ pattern: legalization was nonexistent under the classical gold standard . . . [and] peaked between 1946 and 1971.” Id. at 600.

29 Downs, George W. et al., Is the Good News About Compliance Good News About Cooperation? 50 Int’l Org. 379, 383 (1996)Google Scholar.

30 See Vienna Convention on the Law of Treaties, supra note 15, Arts. 19–23 (dealing with reservations to treaties).

31 Individualized assessments require extensive attention to specific national policies—an endeavor that is enormously, even paralyzingly complicated. However, some general claims about the distribution of depth are plausible. Powerful states are likely to be able to shape commitments to their liking. Consequently, generalized assessments of agreement depth should usually mask the bearing of more depth by weaker states and less depth by stronger states. States whose commitments in an agreement are especially deep are less likely to participate; those whose commitments are especially shallow are most likely to participate.

32 World Trade Organization, The Legal Texts: The Results of the Uruguay Round of Multilateral Trade Negotiations (1999), available at <http://www.wto.org>>Google Scholar [hereinafter Legal Texts].

33 Downs et al., supra note 29, at 391–92.

34 Treaty on the Non-Proliferation of Nuclear Weapons, July 1, 1968, 21 UST483, 729 UNTS 161 (entered into force Mar. 5, 1970).

35 Framework Convention on Climate Change, May 9, 1992, S. Treaty Doc. No. 102–38 (1992), 1771 UNTS 108, available at <http://unfccc.int/2860.php> [hereinafter FCCC].

36 See, e.g., Administrative and Expert Monitoring of International Treaties (Szaszed, Paul C.., 1999)Google Scholar; The Future of U.N. Human Rights Treaty Monitoring (Alston, Philip & Crawford, James eds., 2000)Google Scholar.

37 Raustiala, Kal, Police Patrols & Fire Alarms in the NAAEC , 26 Loy. L.A. Int’l & Comp. L. Rev. 389, 391 (2004)Google Scholar.

38 On the difference, see Anthony, Clark Arend, Legal Rules and International Society 13–39 (1999)Google Scholar; Klabbers, Jan, The Concept of Treaty in International Law 121, 157 (1996)Google Scholar.

39 Ellickson, Robert C., Order Without Law: How Neighbors Settle Disputes (1991)Google Scholar.

40 See, e.g., Posner, Eric A., Law and Social Norms (2000)Google Scholar; Conference, Social Norms, Social Meaning, and the Economic Analysis of Law, 27 J. Legal Stud. 537 (1998)Google Scholar.

41 Agreements are rarely (if ever) labeled soft law. Instead, analysts claim that they are soft law. The idea goes back decades. Even in 1983 Sir Joseph Gold could write, “The concept of ‘soft law’ in international law has been familiar for some years, although its precise meaning is still debated.” Gold, Joseph, Strengthening the Soft International Law of Exchange Arrangements , 77 AJIL 443, 443 (1983)CrossRefGoogle Scholar; see also Ignaz, Seidl-Hohenveldern, International Economic “Soft Law,” 163 Recueil Des Cours 165 (1979 II)Google Scholar.

42 The categories of substance and structure in my framework are clearly continuous in nature; I only dichotomize them for analytical clarity. The category of legality is different. As Klabbers notes, Hume wrote that “[h]alf rights and obligations, which seem so natural in common life,” are “perfect absurdities” when it comes to the law. Klabbers, Jan, The Redundancy of Soft Law , 65 Nordic J. Int’l L. 167, 167 (1996)CrossRefGoogle Scholar; see also Weil, Prosper, Towards Relative Normativity in International Law? 77 AJIL 413 (1983)CrossRefGoogle Scholar.

43 For example, Bilder argues that the concept of soft law is dangerous in that it “depreciated] the currency of law. Bilder, Richard, Beyond Compliance: Helping Nations Cooperate, in Non-Binding Norms, supra note 4, at 65, 72 Google Scholar; see also Weil, supra note 42.

44 Negotiators rarely, if ever, label accords “soft law.” On the importance of the distinction to governments, see Bilder, supra note 43; Weil, supra note 42. But see Ratner, Steven R., Does International Law Matter in Preventing Ethnic Conflict? 32 N.Y.U.J. Int’l L. & Pol. 591, 661–63 (2000)Google Scholar (suggesting that many government officials are unaware of the hard-soft distinction and, moreover, often do not care about that distinction).

45 There are occasional hard cases, such as Maritime Delimitation and Territorial Questions Between Qatar and Bahrain (Qatar v. Bahr.), 1995 ICJ Rep. 6 (Feb. 15) (ICJ holding that an exchange of notes between Qatar and Saudi Arabia and Bahrain and Saudi Arabia constituted a treaty between Qatar and Bahrain). This case is a favorite of those who claim that the line between binding and nonbinding pacts is not always easy to discern. A treaty between states is clearly binding, however, and hard cases like Qatar involve highly unusual, even unique, arrangements. And as Klabbers illustrates, the cases in which judicial bodies purportedly apply soft law turn out, on inspection, to show otherwise. Klabbers, supra note 42, at 172–77.

46 See Thomas, Daniel C., The Helsinki Effect: International Norms, Human Rights, and the Demise of Communism (2001)Google Scholar; Russell, Harold S., The Helsinki Declaration: Brobdingnag or Lilliput? 70 AJIL 242, 246–49 (1976)Google Scholar (Russell was chief U.S. negotiator); Schlager, Erika B., A Hard Look at Compliance with ‘Soft’ Law: The Case of the OSCE, in Non-Binding Norms, supra note 4, at 346 Google Scholar.

47 European Security Conference Discussed by President Ford, 73 Dep’t St. Bull. 204, 205 (1975)Google Scholar. The Organization for Security and Co-operation in Europe (OSCE), the follow-on organization for the broader Helsinki process, continues to rely on nonbinding commitments. See generally Ratner, supra note 44.

48 Treaty on Strategic Offensive Reductions (SORT), May 24, 2002, U.S.-Russ., 41 ILM 799 (2002), available at <http://www.state.gov/t/ac/trt/18016.htm#1>. The U.S. Senate consented to the Treaty on March 6, 2003, and the Russian Duma on May 14, 2003. See President Putin: Strategic Offensive Reductions Treaty Is Crucial, Pravda, May 13, 2003, available at <http://newsfromrussia.com/main/2003/05/13/46889.html>; Kellerhals, Merle D. Jr., U.S. Senate Unanimously Approves Moscow Treaty (Mar. 7, 2003), available at <http://www.useu.be/Categories/ Defense/Mar0703MoscowTreaty.html>>Google Scholar.

49 Slevin, Peter, Ambitious Nuclear Arms Pact Faces a Senate Examination , Wash. Post, July 7, 2002, at A8 Google Scholar.

50 “This new, legally-binding Treaty codifies the deep reductions announced by President Bush . . . and by President Putin at [the] Summit....” Fact Sheet: Treaty on Strategic Offensive Reductions (May 24, 2002), available at <http://www.whitehouse.gov/news/releases/2002/05/20020524-23.html>.

51 Klabbers, supra note 42, at 179. This intuition, of course, is equally true of domestic legal norms. Some are influential, some pointless or moot, some very effective, some wholly ineffective. None of this is germane to their status as law.

52 e.g., Kratochwil, Friedrich V., Rules, Norms, and Decisions: On the Conditions of Practical and Legal Reasoning in International Relations and Domestic Affairs 200–01 (1989)Google Scholar (noting that “it is highly significant that the hardness or softness of [rules] can no longer be derived simply from the formality or genesis of the instrument”); see also Boyle, supra note 26, at 906–07; Pierre-Marie, Dupuy, Soft Law and the International Law of the Environment , 12 Mich. J. Int’l L. 420, 429–30 (1991)Google Scholar; Weiss, supra note 26, at 3.

53 “Sometimes the term ‘soft law’ also refers to the provisions in binding international agreements that are hortatory rather than obligatory.” Weiss, supra note 26, at 3.

54 Kratochwil, supra note 52, at 203.

55 Chinkin, Christine M., The Challenge of Soft IMW: Development and Change in International Law , 38 Int’l & Comp. L.Q. 850, 851 (1989)Google Scholar; see also Ratner, supra note 44, at 614-15; Shelton, supra note 27, at 4 (referring to the “[rjecent inclusion of soft law commitments in hard law instruments”). Paul Szasz likewise claimed that soft law includes “hortatory rather than obligatory language contained in an otherwise binding instrument.” Szasz, Paul C., General Law-Making Processes, in The United Nations and International Law 27, 32 (Joynered, Christopher C.., 1997)Google Scholar.

56 International Covenant on Economic, Social and Cultural Rights, Dec. 19, 1966, Art. 19, 993 UNTS 3, 10.

57 Kaplow, Louis, Rules Versus Standards: An Economic Analysis , 42 Dukel J. 557 (1992)Google Scholar; Sunstein, Cass R., Problems with Rules , 83 Cal. L. Rev. 953 (1995)CrossRefGoogle Scholar.

58 The Hostage Act, for instance, requires the president to “use such means, not amounting to acts of war and not otherwise prohibited by law as he may think necessary and proper” to obtain the release of a U.S. citizen held hostage by a foreign government. 22 U.S.C.S. §1732 (2005). Likewise, the National Environmental Policy Act requires the use of “all practicable means . . . to improve and coordinate Federal plans, functions, programs and resources.” 42 U.S.C. §4331(b) (2000 & Supp. 1 2002).

59 Trachtman, Joel P., The Domain of WTO Dispute Resolution , 40 Harv. Int’l L.J. 333, 337–38 (1999)Google Scholar. Another example is the arbitral award construing “best efforts” in die U.S.-UK Air Services Agreement. Witten, Samuel M., The U.S.-UK Arbitration Concerning Heathrow Airport User Charges , 89 AJIL 174, 176 (1995)Google Scholar.

60 Dennis, Michael J. & Stewart, David P., Justiciability of Economic, Social, and Cultural Rights: Should There Be an International Complaints Mechanism to Adjudicate the Rights to Food, Water, Housing, and Health ? 98 AJIL 462 (2004)CrossRefGoogle Scholar.

61 Many rules of constitutional law have little prospect of judicial enforcement. Yet we do not consider these rules to be “soft law.” There is no jurisprudential reason to treat international legal rules differently.

62 R. R. Baxter, for example, wrote that some commitments had the “characteristic of not creating legal obligations which are susceptible of enforcement, in whatever sense the concept of ‘enforcement’ is employed. They are all ‘soft’ law.” Baxter, supra note 14, at 554.

63 Brunnée & Toope, supra note 6; see also Nino, Carlos S., The Duty to Punish Past Abuses of Human Rights Put into Context: The Case of Argentina , 100 Yale L.J. 2619, 2621 (1991)Google Scholar (“[A] necessary criterion for the validity of any [legal rule] . . . is the willingness of. . . states and international bodies . . . to enforce it.”).

64 See, for example, the instructive table on international norms and institutions from the perspective of regime theorists and international lawyers, in Anne-Marie, Slaughter Burley, International Law and International Relations Theory: A Dual Agenda , 87 AJIL 205, 220 (1993)Google Scholar.

65 Likewise, it is essential to recognize that legal and political agreements are quite closely aligned but nonetheless empirically and causally distinct. In this sense my argument draws on the Oppenheimian tradition. See, e.g., Kingsbury, Benedict, Legal Positivism as Normative Politics: International Society, Balance of Power and Lassa Oppenheim’s Positive International Law , 13 Eur. J. Int’l L. 401, 403 (2002)Google Scholar.

66 Kahler, supra note 28, at 661.

67 Fourth World Conference on Women, Beijing Declaration and Platform for Action, Sept. 15, 1995, UN Doc. A/CONF.177/20 & Add.1 (1995).

68 As the Basel Committee, which negotiated the Basel Accord and Basel II, supra note 22, makes clear, “The Committee does not possess any formal supranational supervisory authority, and its conclusions do not, and were never intended to, have legal force” (emphasis added). The Basel Committee on Banking Supervision (n.d.), available at <http://www.bis.org/bcbs/aboutbcbs.htm>.

69 The various human rights conventions arguably build on and extend the Universal Declaration of Human Rights, which is nonbinding. See Universal Declaration of Human Rights, GA Res. 217A (III), UN Doc. A/810, at 71 (1948).

70 Goldsmith & Posner, supra note 26, at 116.

71 As the late Abram Chayes liked to say, political scientists fear using the “L word.” That fear is fading. See, e.g., Legalization and World Politics (Goldstein, Judith et al. eds., 2001)Google Scholar; Koremenos, Barbara, Loosening the Ties That Bind: A learning Model of Agreement Flexibility , 55 Int’l Org. 289, 290–91 (2001)Google Scholar.

72 The functional claims in the literature are remarkably uniform. See, e.g., Bilder, supra note 3; Abbott, Kenneth W. & Snidal, Duncan, Hard and Soft Law in International Governance , 54 Int’l Org. 421 (2000)CrossRefGoogle Scholar; Aust, supra note 2; Boyle, supra note 26; Goldsmith & Posner, supra note 26; Hillgenberg, supra note 2; Lipson, supra note 11; Weiss, supra note 26; see also Chinkin, supra note 55; Dupuy, supra note 52; Mary, Ellen O’Connell, The Role of Soft Law in a Global Order, in Non-Binding Norms, supra note 4, at 100 Google Scholar.

73 Keohane, Robert O., After Hegemony: Cooperation and Discord in the World Political Economy 80 (1984)Google Scholar.

74 Hillgenberg, supra note 2, at 501.

75 Lipson, supra note 11.

76 Id.; see also Downs, George W. & Rocke, David M., Optimal Imperfection? Domestic Uncertainty and Institutions in International Relations (1995)Google Scholar; Koremenos, supra note 71; Simmons, Beth A., International Efforts Against Money Laundering, in Non-Binding Norms, supra note 4, at 244 Google Scholar, 262 (noting that the use of pledges “may be the most appropriate way to deal with rapidly changing financial practices and market conditions”) .

77 Lipson, supra note 11, at 519–20; see also Koremenos, supra note 71; Simmons, supra note 76, at 262. There are arms control pacts that are pledges, especially in the areas of technology export controls. Gualtieri, David S., The System of Non-Proliferation Export Controls, in Non-Binding Norms, supra note 4, at 467 Google Scholar; see also Angelova, Anastasia A., Compelling Compliance with International Regimes: China and the Missile Technology Control Regime , 38 Colum . J. Transnat’l L. 420 (1999)Google Scholar.

78 Abbott & Snidal, supra note 72, at 423, 438 (stressing the costs associated with delegation); see also Birnie, P. W., Legal Techniques of Settling Disputes: The “Soft Settlement Approach,” in Perestroika and International Law 177 (Butler, W. E. ed., 1990)Google Scholar; Dupuy, supra note 52, at 429-30; Seidl-Hohenveldern, supra note 41, at 193; Szasz, supra note 55.

79 Goldsmith & Posner, supra note 26, at 130–32.

80 Lipson, supra note 11, at 508; see also Goldsmith & Posner, supra note 26, at 124–25; Guzman, Andrew T., The Cost of Credibility: Explaining Resistance to Interstate Dispute Resolution Mechanisms , 31J. Legal Stud. 303 (2002)CrossRefGoogle Scholar.

81 Martin, Lisa L., The United States and International Commitments: Treaties as Signaling Devices (2003)Google Scholar (unpublished manuscript, on file with author).

82 e.g., Downs et al., supra note 29.

83 A category similar to contracts, but with focus on precision and delegation as well.

84 Abbott & Snidal, supra note 72, at 429–30. In the international relations literature, opportunism refers to deliberate noncompliance (or cheating) in a prisoner’s dilemma or in other analogous situations.

85 The incentive to defect is not zero. Some coordination games create incentives for one party to defect publicly to move the equilibrium. In general, however, “no incentive exists for surreptitious cheating. Since the point of diverging from an established equilibrium is to force joint movement to a new one, defection must be public.” Martin, Lisa L., The Rational State Choke of Multilateralism, in Multilateralism Maiters: The Theory and Praxis of an Institutional Form 91, 102 (John, Gerard Ruggie ed., 1993)Google Scholar. Coordination games refer to situations in which no party has an incentive to defect surreptitiously from the agreed standard, though there may be disagreement about the choice of the standard. A common example is driving on the right or the left: no party has an incentive to deviate once the standard has been chosen.

86 FCCC, supra note 35.

87 The Kyoto Protocol is an amendment to the FCCC. It was opened for signature on March 16, 1998, and came into force on February 16, 2005. Kyoto Protocol to the United Nations Framework Convention on Climate Change, Dec. 10, 1997, UN Doc. FCCC/CP/1997/7/Add.2, available at <http://unfccc.int/resource/docs/convkp/kpeng.html>.

88 Forest Principles Statement, supra note 23.

89 Lipson, supra note 11, at 519–20.

90 Cartagena Protocol on Biosafety to the Convention on Biological Diversity, Jan. 29, 2000, 39 ILM 1027 (2000), available at <http://www.biodiv.org/>>Google Scholar.

91 Safrin, Sabrina, Treaties in Collision ? The Biosafety Protocol and the World Trade Organization Agreements , 96 AJIL 606, 628 (2002)Google Scholar.

92 Convention on Biological Diversity, June 5, 1992, 1760 UNTS 79, available at <http://www.biodiv.org/>.

93 International Covenant on Civil and Political Rights, Dec. 16, 1966, 999 UNTS 171 [hereinafter ICCPR].

94 In part, the choice of a contract for the ICCPR may reflect the prior existence of a pledge, in the form of the 1948 Universal Declaration of Human Rights. See note 69 supra.

95 Transgovernmental networks of regulators, for instance, frequently employ pledges and tend to be most active among states that are broadly similar in preferences and regulatory approaches. Raustiala, supra note 8.

96 On the “30% Club,” see text at notes 195–96 infra. On the Paris Club, see its Web site, <http://www.dubdeparis.org>.

97 See Williamson, Richard L. Jr., International Regulation of Land Mines, in Non-Binding Norms, supra note 4, at 505, 517 Google Scholar. Pledges in the arms control area are concentrated in the export control arena, which Williamson considers distinct. Williamson notes that “there are no non-binding instruments negotiated by the relevant parties that would constitute a soft law arms control instrument.” Id. at 517; see also Gualtieri, supra note 77 (discussing export control regimes and noting that the Non-Proliferation Treaty and the 1972 Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on Their Destruction, Apr. 10, 1972, 26 UST 583, 1015 UNTS 163, are binding, but that supplier group arrangements such as the Zannger Committee and Nuclear Supplier Group are not).

98 For example, the Chicago Convention on International Civil Aviation is a contract. Convention on International Civil Aviation, Dec. 7, 1944, 61 Stat. 1180, 15 UNTS 295, available at <http://www.icao.int/cgi/goto_m.plPicao/en/takeoff’.htm>.

99 See Plaza Accord, supra note 21; Basel Accord & Basel II, supra note 22.

100 Hence, I am not claiming that functional accounts are fatally flawed. Rather, “domestic politics complements . . . functionalist explanations for legalization by supplying an explanation for government preferences.” Kahler, supra note 28, at 667.

101 Moravcsik, Andrew, Taking Preferences Seriously: A Liberal Theory of International Politics , 51 Int’l Org. 513 (1997)CrossRefGoogle Scholar; Anne-Marie, Slaughter, International Law in a World of Liberal States , 6 Eur. J. Int’l L. 503 (1995)Google Scholar.

102 “States first define preferences—a stage explained by liberal theories of state-society relations. Then they debate, bargain, or fight to particular agreements—a second stage explained by realist and institutionalist (as well as liberal) theories of strategic interaction.” Moravcsik, supra note 101, at 544.

103 Id. at 523–24.

104 Bilder, supra note 3, at 7–10; Chayes, Abram & Antonia, Handler Chayes. The New Sovereignty : Compliance with International Regulatory Agreements 1–28 (1995)Google Scholar; Raustiala & Slaughter, supra note 5.

105 Downs & Rocke, supra note 76, at 16.

106 Kahler, supra note 28, at 675, uses a similar concept of “compliance constituencies.”

107 See Cassel, Douglass, Inter-American Human Rights IJIW, Soft and Hard, in Non-Binding Norms, supra note 4, at 393 Google Scholar; O’Connell, supra note 72; Shelton, supra note 27, at 9–10; Williamson, supra note 96; cf. Chinkin, Christine M., Normative Development in the International Legal System, in Non-Binding Norms, supra note 4, at 21 Google Scholar, 31 (arguing that nongovernmental organizations “view the soft/hard law distinction as carrying little weight”).

108 Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on Their Destruction, Sept. 18, 1997, 36 ILM 1507 (1997), available at <http://www.icrc.org>.

109 Williamson, supra note 97.

110 Ryan, Michael P., Knowledge Diplomacy: Global Competition and the Politics of Intellectual Property (1998)Google Scholar;see Agreement on Trade-Related Aspects of Intellectual Property Rights, Apr. 15, 1994, Marrakesh Agreement Establishing the World Trade Organization, Annex 1C, reprinted in Legal Texts, supra note 32, at 321.

111 See, e.g., Ratner, supra note 44, at 653 (arguing that there is “an implicit assumption that hard law will affect behavior more than will soft law”).

112 See Stevens, William K., Lessons of Rio: A New Prominence and an Effective Blandness , N.Y. Times, June 14, 1992 Google Scholar, §1, at 10 (“Environmentalists attacked the [nonbinding forest principles] as hopelessly weak, even a step backward . . . “ ) . This view has changed little over the intervening decade. See, e.g., Adebowale, Maria et al., Environment and Human Rights: A New Approach to Sustainable Development (Int’l Inst, for Env’t & Dev., May 2001), available at <http://www.iied.org/docs/wssd/bp_envrights.pdf>Google Scholar (noting that “(‘soft law’) treaties such as the Rio agreements are an inadequate basis for effective control of [globalization]”).

113 Shelton, Dinah, Commentary and Conclusions, in Non-Binding Norms, supra note 4, at 449, 458 Google Scholar. That, said, pledges are common in the International Labour Organization system.

114 Shelton, supra note 27, at 9–10.

115 Cassel, supra note 107, at 401.

116 Domestic preferences are asymmetric in another dimension. There are always domestic actors that oppose cooperation as well as those that prefer it. Those that prefer a new agreement to the status quo (which may or may not be “no agreement”) generally demand a contract. But it does not follow that domestic actors that prefer the status quo therefore demand pledges. Rather, there are three relevant choices: pledges, contracts, and no agreement. While there is little empirical evidence, it appears to be rare for domestic actors to demand pledges as a first-best choice. And domestic actors opposed to new cooperation generally oppose any pact at all, though they may ultimately prefer a pledge to a contract.

117 According to David Sloss, some 25% of global treaties, as opposed to bilateral or regional treaties, submitted to the Senate between 1993 and 2000 were rejected. Sloss, David, International Agreements and the Political Safeguards of Federalism , 55 Stan. L. Rev. 1963, 1984–85 (2003)Google Scholar.

118 Case-Zablocki Act, 1972, 1 U.S.C.S. § 112b(a) (2005). The United Kingdom has a similar rule: pledges do not have to be published, whereas contracts do. Aust, supra note 2, at 789–90.

119 U.S. Dep’t of State, International Agreements, Coordination, Reporting and Publication oflnternational Agreements, 22 C.F.R. §181.2(1) (2005).

120 A set of states may also choose to negotiate a pledge so as to avoid registration with the United Nations, pursuant to Article 102 of the UN Charter.

121 Thomas, supra note 46, at 91–156.

122 This phenomenon is similar to, but distinct from, what Lisa Martin has called the “evasion hypothesis.” That is the claim that the president uses sole executive agreements or congressional-executive agreements to circumvent Senate involvement. Martin finds that there is little empirical support for that claim. See generally Martin, Lisa L., Democratic Commitments: Legislatures and International Cooperation (2000)Google Scholar.

123 Cooper, Richard N., Prolegomena to the Choice of an International Monetary System , 29 Int’l Org. 63, 95–96 (1975)Google Scholar; see also Gold, supra note 41.

124 Schultz, Kenneth A., Domestic Opposition and Signaling in International Crises , 92 Am. Pol. Sci. Rev. 829 (1998)CrossRefGoogle Scholar.

125 The dominant view is that the president may terminate treaties without the Senate’s consent. See, e.g., Henkin, Louis, Foreign Affairs and the United States Constitution 211–12 (2d ed. 1996)Google Scholar.

126 In the United States, this is due to the “Charming Betsy” canon of construction. See Bradley, Curtis A., The Charming Betsy Canon and Separation of Powers: Rethinking the Interpretive Role of International Law , 86 Geo. L.J. 479 (1998)Google Scholar.

127 I say “likely” advisedly, since the various studies on national reception of treaties typically do not discuss pledges at all.

128 See generally Cornes, Richard & Sandler, Todd, The Theory of Externalities, Public Goods, and Club Goods (2d ed. 1996)CrossRefGoogle Scholar.

129 Unless the state in question has preponderant power. See, e.g., Steinberg, Richard H., In the Shadow of Law or Power? Consensus-Based Bargaining and Outcomes in the GATT/WTO , 56 Int’l Org. 339 (2002)CrossRefGoogle Scholar.

130 Global Public Goods: International Cooperation in the 21st Century (Kauletal, Inge. eds., 1999)Google Scholar.

131 Chinkin, supra note 55, at 861.

132 The implications of discounting have been heavily addressed in the literature on the European Union. See, e.g., Alter, Karen J., Establishing The Supremacy of European Law: The Making of an International Rule of Law in Europe (2001)Google Scholar; Pierson, Paul, The Path to European Integration: A Historical Institutional Analysis , 29 Comp. Pol. Stud. 123, 135–36 (1996)Google Scholar.

133 The concern for credibility, however, is a functional variable that operates ex ante, but also tends to push governments toward the negotiation of contracts rather than pledges.

134 Several efforts are underway to create extensive data sets of international agreements and their provisions. However, these data sets are nearly always focused on contracts.

133 The ILO has sponsored more than two hundred pledges and approximately the same number of contracts. See Database of International Labour Standards, at <http://www.ilo.org/ilolex/english/recdispl.htm>.

136 Slaughter, supra note 8; Raustiala, supra note 8, at 22.

137 Aust, supra note 2, at 791–92. Aust also argues that pledges are most likely in such technocratic areas of cooperation. Id. at 789, 791.

138 Simmons, supra note 28, at 598–600.

139 The Plaza and Louvre Accords of 1985 and 1987 were attempts at exchange rate and macroeconomic policy coordination. For more on the Plaza Accord, see supra note 21. For more on the Louvre Accord, see Funabashi, Yoichi, Managing the Dollar: From the Plaza to the Louvre (2d ed. 1989)Google Scholar.

140 See, e.g., Financial Action Task Force on Money Laundering, The Forty Recommendations (June 20, 2003), available at <http://www1.oecd.org/fatf/pdf/40Recs-2003_en.pdf>>Google Scholar; Basel Accord and Basel II, supra note 22. On the recent Paris Club Iraqi debt decision, see Paris Club Press Release, supra note 25; Smith, Craig S., Major Creditors Agree to Cancel 80% of Iraqi Debt , N.Y. Times, Nov. 22, 2004, at A6 Google Scholar. The Paris Club agreements are nonbinding, though the creditor nations then typically negotiate binding bilateral accords, based on the Paris Club agreement, with the debtor state.

141 Following the definition in Downs et al., supra note 29.

142 Id.

143 As Simmons argues, “[Governments are hesitant to make international legal commitments if there is a significant risk that they will not be able to honor them in the future. . . . [Commitment is associated with conditions that one can reasonably anticipate will make compliance possible.” Simmons, supra note 28, at 599.

144 Ratner, Steven R., International Law: The Trials of Global Norms , Foreign Pol’y, Spring 1998, at 65, 68 Google Scholar.

145 Henkin, Louis, How Nations Behave: Law and Foreign Policy 47 (2d ed. 1979)Google Scholar.

146 e.g., Abbott & Snidal, supra note 72, at 429.

147 Olson, Mancur, The Logic of Collective Action : Public Goods and the Theory of Groups (1971)Google Scholar.

148 See also Goldstein, Judith & Martin, Lisa L., Legalization, Trade Liberalization, and Domestic Politics: A Cautionary Note , 54 Int’L Org. 603 (2000)CrossRefGoogle Scholar.

149 Shaffer, Gregory C., Defending Interests: Public-Private Partnerships in W.T.O. Litigation (2003)Google Scholar.

150 “Many international NGOs strongly identify with the norms of environmental and human rights regimes but often experience no direct, material harm from their violation.” Mitchell, Ronald B., Sources of Transparency: Information Systems in International Regimes , 42 Int’l Stud. Q. 109, 120 (1998)Google Scholar.

151 Raustiala, Kal & Victor, David G., Conclusions, in The Implementation and Effectiveness of International Environmental Commitments: Theory and Practice 659 (Victor, David G. et al. eds., 1998)Google Scholar [hereinafter Implementation and Effectiveness].

152 The Future of U.N. Human Rights Treaty Monitoring, supra note 36. Oona Hathaway’s argument about human rights treaties rests critically upon relaxation of pressure by nonstate actors on states that sign and ratify agreements, leading, in some cases, to backsliding in behavior. Hathaway, Oona A., Do Human Rights Treaties Make a Difference? 111 Yale L. J. 1935 (2002)CrossRefGoogle Scholar; cf. Goodman, Ryan & Jinks, Derek, Measuring the Effects of Human Rights Treaties , 14 Eur.J. Int’l L. 171 (2003)Google Scholar.

153 One exception is the 1988 Toronto declaration on climate change. Environment Canada Conference Statement, The Changing Atmosphere: Implications for Global Security? (1988) (available from World Meteorological Organization); see Rowlands, Ian H., The Politics of Global Atmospheric Change 190–92 (1995)Google Scholar.

154 The WTO permits suspension of benefits by a wronged party in the event of noncompliance with an Appellate Body ruling. This is tantamount to exclusion from a subset of the regime’s benefits, i.e., market access in the wronged state.

155 This point is true of trade regimes as well. But as a political matter, rather than an economic one, it has little traction.

156 Downs et al„ supra note 29, at 380–81.

157 I consider the Geneva Conventions to be reciprocity based in a structural/political, rather than a legal, sense. Geneva Convention [I] for the Amelioration of the Condition of the Wounded and Sick in Aimed Forces in the Field, Aug. 12, 1949, 6 UST 3114, 75 UNTS 31; Geneva Convention [II] for the Amelioration of the Condition of the Wounded, Sick, and Shipwrecked Members of Armed Forces at Sea, Aug. 12, 1949, 6 UST 3217, 75 UNTS 85; Geneva Convention [III] Relative to the Treatment of Prisoners of War, Aug. 12, 1949, 6 UST 3316, 75 UNTS 135; Geneva Convention [IV] Relative to the Protection of Civilian Persons in Time of War, Aug. 12, 1949, 6 UST 3516, 75 UNTS 287.

158 e.g., Hathaway, supra note 152, at 2004–11.

159 See, e.g., Keohane, Robert O., Reciprocity in International Relations , 40 Int’l Org. 1 (1986)Google Scholar; Martin, Lisa L., The Political Economy of International Cooperation, in Global Public Goods, supra note 130, at 51 Google Scholar.

160 Andrew Guzman argues that sanctions are rare in part because they represent “a net loss to the parties—one party faces a cost that is not recovered by the other.” Guzman, Andrew T., The Design of International Agreements , 17 Eur. J. Int’l L. (forthcoming 2006)Google Scholar. The theoretical puzzle of why states do not generally provide compensation mechanisms within their international agreements remains to be explained.

161 “A fundamental (and frequent) criticism of international law is the weakness of mechanisms of enforcement.” Lori, Fisler Damrosch, Enforcing International Law Through Non-Forcible Measures , 269 Recueil des Cours 9, 19 (1997)Google Scholar.

162 Buergenthal, Thomas, Proliferation of International Courts and Tribunals: Is It Good or Bad? 14 Leiden J. Int’l L. 267 (2001)CrossRefGoogle Scholar; Symposium, The Proliferation of International Tribunals: Piecing Together the Puzzle , 31 N .Y.U.J. Int’l L. & Pol. 679–933 (1999)Google Scholar.

163 Alter, supra note 132, at 211–32.

164 Weiler, J. H. H., A Quiet Revolution: The European Court of Justice and Its Interlocutors , 26 Comp. Pol. Stud. 510, 519 (1994)Google Scholar.

165 “According to the requirements of most, if not all legal systems, a judgment not only has to contain at a minimum the ‘decision’ reached but has also to provide reasons in support of the particular choice made by the judges.” Kratochwil, supra note 52, at 212.

166 See Arend, supra note 38, at 129–33; Jutta, Brunnée, The Kyoto Protocol: Testing Ground for Compliance Theories? 63 Heidelberg J. Int’l L. 255, 261 (2003)Google Scholar.

167 Milgrom, Paul R. et al., The Role of Institutions in the Revival of Trade: The Law Merchant, Private Judges, and the Champagne Fairs , 2 Econ. & Pol. 1 (1990)Google Scholar.

168 Id. at 19; see also James, McCall Smith, The Politics of Dispute Settlement Design: Explaining legalism in Regional Trade Pacts , 54 Int’l Org. 137, 138 (2000)Google Scholar (asserting that legalized dispute settlement in trade accords “tends to improve compliance by increasing the costs of opportunism”).

169 Chayes & Chayes, supra note 104, at 1-28.

170 Mitchell, supra note 150.

171 Chayes & Chayes, supra note 104; Raustiala & Victor, supra note 151.

172 Simmons, supra note 76, at 261 (“The key to the FATF’s success seems to flow from the serious and sustained attention the organization gives to monitoring and assessment.”); see also note 140 supra.

173 Helsinki Final Act, supra note 20, Follow-up to the Conference, 14 ILM at 1325, para. 2(a).

174 Schlager, supra note 46, at 355.

175 The official OSCE Handbook notes that “the fact that OSCE commitments are not legally-binding does not detract from their efficacy. Having been signed at the highest political level, they have an authority that is arguably as strong as any legal statute under international law.” OSCE Secretariat, The Handbook of the Organization for Security and Co-operation in Europe (OSCE) 3 (3ded. 2002), available at <http://www.osce.org/>.

176 Simmons, supra note 76, at 262.

177 Realists might argue that pledges are simply what political scientists call “cheap talk”: symbolic, costless action. Cheap talk can become a self-perpetuating equilibrium outcome; for example, all job applicants claim to be hardworking since, if they failed so to state, it would make them stand out. In such a “pooling equilibrium” all actors behave the same way, by engaging in cheap talk pledge-making. But this is unlikely in the case of multilateral pledges. They are too cosdy, both in transaction costs and in risking the incitement of political action, to be negotiated simply to avoid not negotiating them.

178 Chinkin, supra note 56, at 860; Dupuy, supra note 52.

179 Smith, supra note 168, at 148.

180 Patrick, Széll, The Development of Multilateral Mechanisms for Monitoring Compliance , in Sustainable Development and International Law 97, 107 (Langed, Winfried., 1995)Google Scholar; see also Shelton, supra note 27, at 15 (“It may even be possible that some stronger monitoring mechanisms exist in soft law precisely because it is non-binding and states are therefore willing to accept the scrutiny they would reject in a binding text.”); Simmons, supra note 76.

181 Abbott, Kenneth W., “Trust but Verify”: The Production of Information in Arms Control Treaties and Other International Agreements, 26 Cornell Int’l L.J. 1, 36–38, 53–54 (1993)Google Scholar.

182 Raustiala & Victor, supra note 151.

183 For another view in this issue on the effectiveness of nonbinding agreements, see Mirmina, Steven A., Reducing the Proliferation of Orbital Debris: Alternatives to a Legally Binding Instrument , 99 AJIL 649 (2005)CrossRefGoogle Scholar.

184 A completely shallow agreement—one that simply ratified the status quo ante—would not be effective at all, since it would not change state behavior. As I noted earlier, this claim can be challenged by the fact that an accord may be aimed at forestalling future backsliding; an example would be the Non-Proliferation Treaty. But aside from this, shallow agreements, even when perfectly complied with, are by definition ineffective (or have little effectiveness) since they do not demand that states deviate from prior behavior. If such a shallow agreement induced overcompliance for some reason, that agreement would plausibly be called effective.

185 Goldstein & Martin, supra note 148, at 631–32.

186 I owe much to the perceptive thinking of David Victor on this issue.

187 Goldstein & Martin, supra note 148; Raustiala & Slaughter, supra note 5.

188 Goldstein & Martin, supra note 148, at 622.

189 See, e.g., Ho, supra note 4; Taring, David, International Law by Other Means: The Twilight Existence of International Financial Regulatory Organizations , 33 Tex. Int’l L.J. 281, 282, 287–92 (1998)Google Scholar.

190 Schlager, supra note 46, at 353–54; see also Ratner, supra note 44, at 610 (arguing that the OSCE experience suggests that soft law commitments may be more valuable and effective than commonly believed).

191 Shine, Clare, Selected Agreements Concluded Pursuant to the Convention on the Conservation of Migratory Species of Wild Animals, in Non-Binding Norms, supra note 4, at 196, 222 Google Scholar; see also Edith, Brown Weiss, Understanding Compliance with International Environmental Law: A Baker’s Dozen Myths , 32 U. Rich. L. Rev. 1555 (1999)Google Scholar.

192 See Jon, Birger Skjaerseth, The Making and Implementation of North Sea Commitments: The Politics of Environmental Participation, in Implementation and Effectiveness, supra note 151, at 327 Google Scholar.

193 Id.

194 Protocol to the 1979 Convention on Long-Range Transboundary Air Pollution Concerning the Control of Emissions of Nitrogen Oxides and Their Transboundary Fluxes, Oct. 31, 1988, available at <http://www.unece.org/env/lrtap>.

195 Levy, Marc A., European Acid Rain: The Power of Tote-Board Diplomacy, in Institutions for the Earth: Sources of Effective International Environmental Protection 75 (Haas, Peter M. et al. eds., 1993)Google Scholar.

196 Jørgen, Wettested, Participation in NOx Policy-Making and Implementation in the Netherlands, UK, and Norway: Different Approaches but Similar Results’? in Implementation and Effectiveness, supra note 151, at 381 Google Scholar.

197 International Environmental Law and Policy 999–1000 (Hunter, David et al. eds., 2d ed. 2002)Google Scholar. For the text, see La Jolla Agreement for the Reduction of Dolphin Mortality in the Eastern Pacific Ocean, Apr. 1992, available at <http://www.oceanlaw.net/texts/lajolla.htm>.

198 Raustiala & Victor, supra note 151, at 659–707.

199 On the Marshall Plan as a model, see Schelling, Thomas C., The Cost of Combating Global Warming , Foreign Aff., Nov./Dec. 1997, at 8, 10–12 Google Scholar.

200 Id.at 10.

201 See, e.g., Raustiala & Victor, supra note 151, at 689-97. For a skeptical take, see José E., Alvarez, Do Liberal States Behave Better? A Critique of Slaughter’s Liberal Theory , 12 Eur. J. Int’l L. 183, 246 (2001)Google Scholar.

202 See, e.g., Helfer, Laurence R., Overlegalizing Human Rights: International Relations Theory and the Commonwealth Caribbean Backlash Against Human Rights Regimes , 102 Colum. L. Rev. 1832 (2002)CrossRefGoogle Scholar.

203 Goldstein & Martin, supra note 148, at 603–04.

204 Nevertheless, international courts often show themselves to be politically astute. In the context of the WTO Appellate Body, see Sternberg, Richard H., Judicial Lawmaking at the WTO: Discursive, Constitutional, and Political Constraints , 98 AJIL 247 (2004)CrossRefGoogle Scholar.

205 The withdrawal by the United States of its signature of the Rome Statute is an example of a state’s decision not to participate because of ex ante concerns about overlegalization.

206 Slaughter, supra note 8; Raustiala, supra note 8.