Contemporary world politics is a matter of wealth and poverty, life and death. This chapter aims to evaluate the strengths and weaknesses of the rationalistic approach, taking into account the criticisms put forward by scholars who emphasize how actors are constituted by institutions and how subjective self-awareness of actors, and the ideas at their disposal, shape their activities. It discusses the critical importance, for the further advance of knowledge, of undertaking empirical research, guided by the theoretical ideas. "Institution" is an even fuzzier concept than cooperation. Rationalistic research on international institutions focuses almost entirely on specific institutions. It emphasizes international regimes and formal international organizations. A major challenge for students of international relations is to obtain such knowledge of institutions, through theory and the application of theory to practice, but especially through empirical research. Both rationalistic and reflective approaches need further work if they are to become well-developed research programs.