The interplay between states and international organizations has received a lot of scholarly attention, largely because the number of international organizations has increased considerably within the last century. State-of-the-art scholarship on the foreign policies of international organizations and states is presented here, as are rationalist and constructivist accounts of how the foreign policies of states impact international organizations (bottom-up perspective), as well as how, in turn, international organizations impact member-state foreign policies (top-down perspective). Thereby, the polity, politics, and policy dimensions of both states and international organizations are examined in order to explain the changes states’ foreign policies can induce, under what scope conditions, in the international organizations’ structure (polity), procedures (politics), and policy outcomes. Vice versa, also explained are the changes international organizations can induce, under what scope conditions, in the foreign policy apparatus of states (polity), foreign policy decision-making procedures (politics), and states’ foreign policies. As is illustrated, the theme “International Organizations and Foreign Policy” is not an established foreign policy subfield per se but is covered here in multiple approaches and theories. In line with the development of international relations, the bottom-up perspective has received much more scholarly attention than the top-down perspective. Furthermore, bottom-up research evidences a tendency toward the strong influence of states’ foreign policies on the policy and polity of international organizations, while the top-down influence of international organizations on states’ foreign policy apparatus, procedures, and policies is usually much more limited. Finally, an outlook into fruitful future avenues for research is outlined.