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 defined multilateralism as "the practice of coordinating national policies in groups of three or more states."
John Ruggie elaborated the concept 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 powerful nations, discourage unilateralism, and gives small powers a voice and influence that they could not otherwise exercise. For a small power to influence a great power, the Lilliputian strategy of small countries banding together to collectively bind a larger one can be effective. Similarly, multilateralism may allow one great power to influence another great power. For a great power to seek control through bilateral ties could be costly; it may 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.