Liberalism is the dominant political philosophy of our times. The main purpose of this book is to defend a "perfectionist" account of liberalism, one that holds that the state should promote the flourishing of all who are subject to its power, even when doing so requires it to take sides between controversial views of the good life. This book provides a comprehensive and up to date discussion of liberalism and perfectionism and deals with some of the most fundamental issues in contemporary liberal political philosophy.