In its simplest form, multilateralism is a method of diplomacy that considers diplomatic partners several at a time. Bilateralism, by contrast, deals with other countries one by one. Multilateralism can be formal, involving treaty organizations and other multinational institutions; it can also be informal, based simply on an appreciation of how particular events affect several nations simultaneously. In practice the formal and informal entwine; a network of explicit commitments and implicit understandings knit together the participating nations and constrain their actions.

Relations between the United States and Germany since World War II provide a good example of the formal and informal aspects of multilateralism. Formal elements took precedence first, but as the memories of the war faded and the two sides gained confidence in each other, informal multilateralism grew more important. At the same time, the purposes of multilateralism for the two governments changed along with the relative strength of the military, political, economic, and cultural aspects of their relationship. For Washington, multilateralism was initially a method of tying Germany down and binding Bonn to the West; later it became a way of encouraging the Germans to contribute to European security. For Bonn, multilateralism at first served as an alternative to indefinite occupation; later it became an avenue for Germany's reemergence as the leading power in Europe.