By reading written and visual artefacts of Gertrude Stein’s life, Gertrude Stein’s Transmasculinity reframes earlier scholarship to argue that her gender was transmasculine and that her masculinity was positive rather than a self-hating form of false consciousness. This book considers ways Stein’s masculinity was formed through her relationship with her feminine partner, Alice B. Toklas, and her masculine homosocial bonds with other modernists in her network. This broadens out Eve Kosofsky Sedgwick’s account of “male homosocial bonding” to include all masculine persons, opening up the possibility of examining Stein’s relationship to Toklas; masculine women such as Jane Heap; and men such as Pablo Picasso, Ernest Hemingway, and Carl Van Vechten. The Introduction and first four chapters focus on surfacings of Stein’s masculinity within the visual and the textual: in others’ paintings and photographs of her person; her hermetic writings from the first three decades of the twentieth century; and her self-packaging for mass consumption in The Autobiography of Alice B. Toklas (1933). Whereas the chapter on The Autobiography underscores Toklas’s role in the formation of Stein’s masculinity and success as a modernist, the final three register the vicissitudes of the homosocial bonds at play in her friendships with Picasso, Hemingway, and Van Vechten. The Coda, which cross-reads Stein’s Everybody’s Autobiography (1937) with the media attention two museum exhibits about her attracted between 2011 and 2012, points to possibilities for future work on the implications of her masculine homosocial bonds with Vichy collaborator Bernard Fäy.