This book is about how politicians govern the experts they put in charge of public decisions. It aims to challenge some common assumptions scholars of governance often make about how experts come to be given power in liberal democratic states, and how subsequently they retain that power. There is a large and sprawling theoretical and conceptual literature on ‘the politics of expertise’ in governance and public policy that demands attention and informs what Andrew Gamble (1990) calls a conceptual ‘map’, which this book uses to frame the empirical case studies. This map does not involve the deduction of hypotheses and their empirical testing; it is a way of framing, in an encompassing manner, the empirical dynamics the book identifies in the following chapters. This map is what the book terms the expert–politics nexus, which refers to diverse political relationships between elected governments and civil servants, and ‘arm’s length’ expert-led agencies. To do so, the book offers a new approach to combining and linking previously disparate approaches to ‘expertise’ in governance research.