This chapter examines the role of expertise in policy-making at different levels of analysis. Expertization comes in many shapes and variants, and contemporary governance systems offer a wide array of channels for supplying expert knowledge to political decision-makers, ranging from expertise in ministries and agencies, via various forms of advisory bodies, to think tanks and consultancies. Expertise plays a somewhat different role within different types of administrative bodies. While policy bureaucracies develop policies, the implementation of these policies and the regulation of different sectors of the economy have increasingly been delegated to a different kind of bureaucratic body, namely agencies. The power of the courts has increased in recent decades as a result of the expansion and specification of legal regulations, a process referred to as juridification.