In this introduction, I address some general conceptual and theoretical issues in the analysis of international socialization and establish some general conditions regarding the impact of international organizations in Central and Eastern Europe. First, I will briefly discuss three literatures to which this book, and the study of the international socialization of Central and Eastern Europe in general, can make a contribution: enlargement, transition, and Europeanization. In the second part, I will address conceptual issues that concern the central items listed in the book title: Who are the “nannies” in Central and Eastern Europe? What are the “norms” they disseminate, teach, or enforce? And how do we conceptualize and measure their domestic “impact”? In the third part of the introduction I will bring up some theoretical issues: What are the main factors and mechanisms of international socialization proposed in the literature? What are the prevalent international and domestic conditions in the international socialization of Central and Eastern Europe, and how do they affect the impact of international organizations in this region? Finally, I will contrast the “model story” of international socialization, according to which the states to be socialized learn and institutionalize the international norms taught by the international organization, with several unintended or counterproductive effects that international socialization may have and for which ample evidence can be found in the studies assembled in this volume.