Brian Cassidy has been involved in the book business in one form or another since 1994. In 2004 he established Brian Cassidy Bookseller, specializing broadly in twentieth-century countercultural and avant garde movements, as well as archival and vernacular materials. He has served on the faculty of the Antiquarian Book Seminar, and is a member of the Antiquarian Booksellers’ Association of America, the International League of Antiquarian Booksellers, the Independent Online Booksellers Association. In June of 2019 he launched with co-founder Rebecca Romney the rare book firm Type Punch Matrix. He has lectured on the bibliography of duplication at Rare Book School, New York University, Yale, Columbia, the University of Pennsylvania, Princeton, and elsewhere.