This chapter outlines the theoretical and empirical puzzles that inform the book, its objectives, overall argument, and structure. It sets out to explain the changing preferences and influence of the UK in shaping multi-level financial regulation. In particular, the book addresses two empirical questions. Why has the UK favoured increasingly stringent regulation in certain financial sectors since the crisis, but not in others? Why has the UK led international and EU-level regulatory reforms in some areas, but has resisted these initiatives in other areas? The chapter also outlines the book’s ambition to undertake a preliminary assessment of the impact of Brexit on the future of UK financial regulation, focused on two questions. Why has the UK decided to withdraw from the EU single market in services, including finance? How is Brexit likely to impact on the UK’s regulatory preferences and ability to shape multi-level financial regulation?