This Chapter examines controversial issues surrounding the design of supervisory institutions for financial markets. It begins by considering the main institutional models identified in the literature and those implemented in selected countries such as Australia, Canada, France, Germany, the UK, and the US. It then discusses the significance of institutional design, the public character of supervision and the role of self-regulation, and the role of central banks in financial supervision. It also analyses the mandates and powers of supervisory agencies, together with supervisory accountability, governance, and transparency. The Chapter concludes by focusing on supervisory costs and funding models, and suggesting that there is no single ‘right’ or ‘wrong’ institutional model for financial supervision.