Canada is a federal state，but the relationship between the central and local government has never adopted a single and standardized model. This state has lived with three distinct models of federalism—three federalisms in one country，each with its own decision rules and intergovernmental processes. These three models are classical federalism，shared-cost federalism and joint-decision federalism. Social policy reflects all three particularly well. Throughout the history of the Canadian welfare state，federal and provincial governments have designed different social programs according to different intergovernmental rules and processes. More precisely，at critical historical junctures，exactly the same federal and provincial governments were shaping different social programs according to different models of federalism，with differing policy outcomes. Canada therefore constitutes a natural laboratory in which to analyze the implications of different models of federalism. The distinctive incentives and constraints inherent in the different models help explain a number of puzzles about the Canadian welfare state，including the striking contrast between the limited nature of the country’s income security programs and the more universalist character of its health care. Moreover，in recent decades，the three models help explain the highly uneven impact of retrenchment on different social programs.