One's assumptions about world politics profoundly affect what one sees and how one constructs theories to explain events. We believe that the assumptions of political realists, whose theories dominated the postwar period, are often an inadequate basis for analyzing the politics of interdependence. The realist assumptions about world politics can be seen as defining an extreme set of conditions or ideal type. One could also imagine very different conditions. In this chapter, we shall construct another ideal type, the opposite of realism. We call it complex interdependence. After establishing the differences between realism and complex interdependence, we shall argue that complex interdependence sometimes comes change reality than does realism. When it does, traditional explanations of change in international regimes become questionable and the search for new explanatory models becomes more urgent.