Utilitarianism - a philosophy based on the principle of the greatest happiness for the greatest number of people - has been hugely influential over the past two centuries. Beyond ethics or morality, utilitarian assumptions and arguments abound in modern economic and political life, especially in public policy. Understanding Utilitarianism presents utilitarianism as a living tradition. Tim Mulgan begins with a summary of the classical utilitarianism of the eighteenth and nineteenth centuries and traces the subsequent development of the central themes of utilitarian thought over the twentieth century, covering such questions as: What is happiness? Is happiness the only valuable thing? Is utilitarianism about acts or rules or institutions? Is utilitarianism unjust, or implausibly demanding, or impractical? Where might utilitarianism go in the future?