Book excerpt: Since the early twentieth century, politically engaged and socially committed U.S. health professionals have worked in solidarity with progressive movements around the world. Often with roots in social medicine, political activism, and international socialism, these doctors, nurses, and other health workers became comrades who joined forces with people struggling for social justice, equity, and the right to health. Anne-Emanuelle Birn and Theodore M. Brown bring together a group of professionals and activists whose lives have been dedicated to health internationalism. By presenting a combination of historical accounts and first-hand reflections, this collection of essays aims to draw attention to the longstanding international activities of the American health left and the lessons they brought home. The involvement of these progressive U.S. health professionals is presented against the background of foreign and domestic policy, social movements, and global politics.