Socialism has made a dramatic comeback in the 21st century. In the wake of financial crisis, mounting inequality and social decay, it seems more relevant than ever. Nobody who seeks to understand contemporary politics can ignore it. In this book, leading scholar Peter Lamb identifies the key ideas and principles of socialism and explores different (often conflicting) interpretations that have appeared in Europe, Asia, Africa and the Americas, from the early nineteenth century until today. He explores the different ways that socialist thinkers have conceptualised community, equality and liberty and shows how, despite overlap with other traditions, socialists have combined these ideas in common and distinct ways that make the socialist tradition uniquely valuable. Lamb goes on to trace the recent re-emergence of these ideas, and explain what will be required for such a revival to be popular, powerful and sustained. This book will be invaluable to any student or scholar interested in political theory, socialism, communism or political ideologies, as well as to general readers striving to understand contemporary politics throughout the world.