Karl Popper is a philosopher of knowledge and politics, rationality and freedom. His ideas have won acceptance and provoked controversy among an academic as well as a more general audience. This book aims to broaden our understanding of Popper's philosophy. It is one of the few studies to present his work as an evolving "system of ideas", and to take account of the full range of his writings. The book discusses Popper's early philosophy of politics, science and social science, as well as his later philosophy, which offers an evolutionary account of human nature and the growth of knowledge. Contrary to many earlier interpretations, Stokes argues that we should look to Popper's political values to understand the unity of his work and the evolution of his theory of knowledge and general philosophy. The chapters in this book examine Popper's arguments, and offer critical analysis of the achievements and shortcomings of his philosophy. In particular, Stokes considers the problems of rationality, politics and ethics in the context of debates between the Frankfurt School of critical theory and critical rationalism. The book will be of interest to second-year undergraduates and above in the fields of philosophy and critical theory.