How should we judge competing explanatory claims in social science research? How can we make inferences about which alternative explanations are more convincing, in what ways, and to what degree? Case study methods—especially methods of within-case analysis such as process tracing— are an indispensable part of the answer to these questions. This chapter offers an overview of process tracing as a tool for causal inference, focusing on the study of international relations, an area rich with examples of this approach. In (...) contrast to the subsequent two chapters in this volume, where Freedman and Brady analyze micro-level examples, the present chapter explores process tracing in macro studies. (shrink)