Ideologies play a crucial role in the way we understand and shape the political world. But no one has yet satisfactorily explained the nature of ideologies themselves. Michael Freeden here offers a ground-breaking approach to the subject. Drawing on the political experience of Britain, France, Germany, and the USA over the past two centuries, the author provides an in-depth examination of the key political ideologies: liberalism, conservatism, socialism, feminism, and green political thought. He outlines a powerful and sophisticated new theory of ideologies, arguing that by paying special attention to the complexity, conceptual inter-relationship, and historical and contemporary context of ideologies we can both better understand them and reinvigorate the study of political theory.