This book builds on recent scholarship highlighted in the edited collections, Philosophie, histoire, biologie: mélanges offerts à Jean Gayon (Merlin & Huneman, 2018) and Knowledge of Life Today (Gayon & Petit 2018/2019). While honoring the career and the thought of Jean Gayon (1949-2018), this book showcases the continued relevance of Gayon’s interdisciplinary work and illustrates his central place in the community of historians and philosophers of the life sciences. Chapters in this book address Jean Gayon’s intellectual trajectory from historical epistemology to the philosophy of biology, the nature and scope of his philosophical approach to the history of science, and his unique contributions to the history and epistemology of biological concepts and theories. Drawing on published and unpublished sources, the book explores some of Gayon’s most significant contributions to the philosophy, history, and social studies of biology.