This chapter motivates the book’s central questions: Why is incumbency an electoral blessing for politicians in some countries but an electoral curse in others? Why does incumbency bias emerge? What are the consequences of incumbency bias for democracy? The chapter then presents the book’s bounded accountability theory in brief: incumbency bias emerges and varies because democratic institutions generate a mismatch between citizens’ expectations of incumbent performance and incumbents’ capacity to deliver. The chapter clarifies how this argument builds and expands upon prior work on incumbency bias in Latin America and the US, and how it draws theoretical insights from theoretical and empirical work on electoral accountability. The chapter also distils contrasting predictions between bounded accountability and theories that stress corruption and clientelism as the drivers of incumbency advantage and disadvantage. The chapter closes by describing the case selection and outlining its nested-multilevel research design that combines cross-country and within-country comparisons and employs tools of causal inference to examine incumbency bias in Argentina, Brazil and Chile.