Alexander Berkman’s 1912 Prison Memoirs of an Anarchist is a significant book in the development of American anti-prison politics, not despite, but because of its ambivalent approach to prisons. I trace through Berkman’s book and archive an unresolved tension between two approaches to the prison: advocacy for political prisoners, whereby the prison is a state tool for suppressing radical ideas, and advocacy against the politics of prisons, whereby the prison is an “aggravated counterpart” of social structures and a site of struggle. Berkman’s ambivalence between these approaches amid his memoirs and activism exemplifies the complex development of U.S. thinking on prisons and enduring tensions in contemporary prison politics.