Let Them Tremble: Biographical Interventions Marking 100 Years of the Communist Party, USA is a collection of six biographies exploring unique and often neglected aspects of the Communist Party, USA (CPUSA). Each biographical intervention explores a specific CPUSA leader's life, work and times and places them within political and historical context. The interventions collectively span the bulk of the Party's history, not just the so-called Heyday, Popular Front, McCarthy or Old Left periods. Special emphasis is placed on Party activity and analysis in the post-1956 period, in the 1960s, 1970s and 1980s, up to the Party's centennial. Each biography consists of two or three overarching themes; the individual narratives largely focus on aspects of Party work as they relate to these themes. The subjects are Arnold Johnson, Charlene Mitchell, Gus Hall, Henry Winston, Judith LeBlanc, and W. Alphaeus Hunton. I have avoided Party leaders who have been given considerable biographical attention by other authors, such as William Z. Foster, Claudia Jones, Ben Davis, Jr., Elizabeth Gurley Flynn, James and Esther Cooper Jackson, William Patterson, and Angela Davis, among others.