This chapter introduces the foundational concepts of sufficient causes (SCs) and causal mechanisms as tools for understanding social change. It begins by distinguishing SCs—conditions that guarantee an effect when present—from necessary causes and explains how causal mechanisms link causes to outcomes by specifying the processes that generate effects under defined background conditions. The chapter then examines “pie causation,” where multiple components cause jointly form an SC, and “fundamental causality,” in which a repertoire of interchangeable mechanisms sustains a stable cause–effect relationship across contexts. Next, it assesses different tests (the “smoking gun” and the “doubly decisive”) for confirming causal claims and discusses the structure of scientific explanation, emphasizing the roles of conceptual frameworks, theories, causal mechanisms, and models, and highlights the importance of analytical ideal types for isolating SCs through counterfactual reasoning. The methodology of Inference to the Best Explanation (IBE) is presented as a rational framework for choosing among competing causal hypotheses by weighing explanatory power, coherence, depth, and simplicity. Finally, the chapter addresses the limits of SC-based analysis in “super-wicked” problems like climate change, where complexity and interdependence impede the isolation of decisive causes.