Multilateralism was defined by Miles Kahler as "international governance" or global governance of the "many," and its central principle was "opposition bilateral discriminatory arrangements that were believed to enhance the leverage of the powerful over the weak and to increase international conflict". In 1990, Robert Keohane simply defined multilateralism as "the practice of coordinating national policies in groups of three or more states. John Ruggie further elaborated the concept of multilateralism based on the principles of "indivisibility" and "diffuse reciprocity (international relations)" as "an institutional form which coordinates relations among three or more states on the basis of 'generalized' principles of conduct ... which specify appropriate conduct for a class of actions, without regard to particularistic interests of the parties or the strategic exigencies that may exist in any occurrence."
Multilateralism, in the form of membership in international institutions, serves to bind the great power, discourage unilateralism, and give the small powers a voice and voting opportunities that they would not otherwise have. Particularly if control is sought by a small power over a great power, the Lilliputian strategy of small countries achieving control by collectively binding the great power is likely to be most effective. Similarly, if control is sought by a great power over another great power, then multilateral controls may be most useful. The great power could seek control through bilateral ties, but this would be costly; it would also require bargaining and compromise with the other great power. Embedding the target state in a multilateral alliance reduces the costs borne by the power seeking control, but it also offers the same binding benefits of the Lilliputian strategy. Furthermore, if a small power seeks control over another small power, multilateralism may be the only choice, because small powers rarely have the resources to exert control on their own. As such, power disparities are accommodated to the weaker states by having more predictable bigger states and means to achieve control through collective action. Powerful states also buy into multilateral agreements by writing the rules and having privileges such as veto power and special status.
International organizations, such as the United Nations (UN) and the World Trade Organization, are multilateral in nature. The main proponents of multilateralism have traditionally been the middle powers, such as Canada, Australia, Switzerland, the Benelux countries and the Nordic countries. Larger states often act unilaterally, while smaller ones may have little direct power in international affairs aside from participation in the United Nations (by consolidating their UN vote in a voting bloc with other nations, for example.) Multilateralism may involve several nations acting together, as in the UN, or may involve regional or military alliances, pacts, or groupings, such as NATO. These multilateral institutions are not imposed on states, but are created and accepted by them in order to increase their ability to seek their own interests through the coordination of their policies. Moreover, they serve as frameworks that constrain opportunistic behavior and encourage coordination by facilitating the exchange of information about the actual behavior of states with reference to the standards to which they have consented.
The term "regional multilateralism" has been proposed, suggesting that "contemporary problems can be better solved at the regional rather than the bilateral or global levels" and that bringing together the concept of regional integration with that of multilateralism is necessary in today’s world. Regionalism dates from the time of the earliest development of political communities, where economic and political relations naturally had a strong regionalist focus due to restrictions on technology, trade, and communications.