Parts of the international institutional order today appear quite robust and adaptive. This is true not only in economic but also in security affairs, and it is true not only in Europe but also at the global level. The reason goes beyond the fact that these are institutions and that institutions are "in demand." A core feature of the international institutional order is its multilateral form. The multilateral form, under certain circumstances, appears to have characteristics that enhance its durability and ability to adapt to change. Yet the concept of multilateralism is poorly defined and therefore poorly understood in the literature. This article recovers its principled meanings from historical practice, shows how and why these principled meanings have come to be institutionalized, and suggests why multilateralism may continue to play a significant role today even as some of the postwar conditions that gave rise to it have changed.
