We open the book by discussing the rise of constitutional courts and judicial review, emphasizing their stated responsibility as guardians of the constitutional system. We discuss existing theories of judicial power and independence, highlighting the concept of judicial efficacy: the ability of courts to create political penalties for elites who fail to abide by the constitutional limits on their authority. We discuss different types of penalties courts might levy and explain why attitudinal costs – particularly a loss of public support – represent the cornerstone of judicial efficacy. We then provide a summary of our argument, contrasting our theory of judicial efficacy with existing accounts of judicial power and impact. The chapter concludes with a roadmap for the rest of the book and a summary of our key findings.