This chapter introduces the book by presenting the main puzzle motivating it – variation in deference. It suggests that international courts defer to varying degrees and through different modes. This chapter presents the book’s conceptual approach to studying deference and the core theoretical argument advanced by the book. In doing so, it distinguished the conceptual and theoretical framework from existing literature on international courts. It describes the research design that guides the empirical analysis and the logic behind the book’s focus on the East African Court of Justice, Caribbean Court of Justice, and the African Court of Human Rights. The chapter briefly summarizes the main findings and the implications of the book for future research.