From 1966 to 1970, historian Martin Duberman transformed his undergraduate Princeton seminar on American radicalism. This book looks closely at the seminar, drawing on interviews with former students and colleagues, conversations with Duberman, and abundant archival material in the Princeton archives and the Duberman Papers. The array of evidence makes the book a primer on how historians gather and interpret evidence while at the same time shining light on the tumultuous late 1960s in American higher education. This book will become a tool for teaching, inspiring educators to rethink the ways in which history is taught and teaching students how to reason historically through sources.