This chapter sets out the debates that have grown up around CEOs, highlighting three major reasons why they warrant serious study: their importance to the companies they lead, their wider economic and political power, and what their careers tell us about social mobility. To address these debates the book explores three questions: Who were the CEOs and how did they get into the role? What did they do? Did they matter for their companies and Britain’s economy and society? To answer these questions, a unique database of the CEOs of the top 100 most valuable UK public companies between 1900 and 2009 has been assembled. This consists of 475 companies and 1,397 CEOs. For each CEO a career biography is created. To analyse the data, we draw on Upper Echelons Theory and Agency Theory, alongside historical scholarship to understand the environments in which they operated. The chapter then sets out the five analytical threads that are developed throughout the book. The chapter closes by discussing how the nomenclature around top corporate officers evolved from ‘chairman’ to ‘managing director’ to ‘chief executive officer’.