There are important differences between constituent units of federal or quasi-federal states in OECD countries with respect to both powers for taxation of personal income and the use made of such powers, if any. Subnational Tax Autonomy in OECD Federations examines tax autonomy as a powerful tool in setting tax rates. Two key issues are examined in detail: first, why proposals giving more power to set tax rates have been implemented (Spain), put forward (UK), stalled (Belguim), or set aside (Germany), and second, how such powers are used in federations whose constituent units have them (Canada, Switzerland, and the United States).