A chapter-by-chapter précis is presented of Randall Collins’s book, The Sociology of Philosophies: A Global Theory of Intellectual Change. It presents a sociological theory of intellectual networks that connect thinkers in chains of masters and pupils, colleagues and rivals, and of the internalized conversations that constitute the social processes of thinking. The theory is used to analyze long-term developments of the intellectual communities of philosophers in ancient Greece, ancient and medieval China and India, medieval and modern Japan, medieval Islam and Judaism, medieval Christendom, and modern Europe through the early 20th century.