Same Sex, Different States: When Same-Sex Marriages Cross State Lines. By Andrew Koppelman. New Haven: Yale University Press, 2006. 224p. $35.00.

America's Struggle For Same-Sex Marriage. By Daniel R. Pinello. New York: Cambridge University Press, 2006. 213p. $55.00 cloth, $19.99 paper.

The landscape of marriage in the United States is changing yet again, driven this time by tensions over the rights of same-sex couples to marry. States across the nation have revisited their laws in recent years to clarify the legal rights and responsibilities of same-sex couples, with widely divergent outcomes. Massachusetts permits same-sex couples to marry, currently the only state to do so. Six other states grant same-sex couples all the state-level rights and benefits of marriage, typically under the name of civil unions. On the flip side, 26 states have amended their constitutions expressly to limit marriage to opposite-sex couples; 17 also bar the establishment or recognition of alternative legal regimes designed to give the substantive rights of marriage to same-sex couples. One additional state, Hawaii, amended its constitution to give the state's legislature the sole ability to decide who may marry, a move that successfully derailed a constitutional challenge to the state's existing marriage regime. The federal government has also gotten into the game. The 1996 Defense of Marriage Act (DOMA) limits marriage to opposite-sex couples for all federal purposes and authorizes states to opt out of recognizing same-sex marriages validly performed in other jurisdictions.