The Reformation reframed the way that people talked about gender, kin, and community. One way in which it did so was to deploy the language of brotherhood and sisterhood in new contexts. Aside from referring to blood relationships, ‘brother’ and ‘sister’ were used in medieval society to designate monastic ties and bonds in fraternal associations. These institutions were fractured during the Reformation, as monasteries and convents were dissolved and fraternities attacked. Yet reformers did not abandon the rhetoric of brotherly and sisterly affection, but used it in new contexts. Brotherhood was used to negotiate relationships between reformers and reforming communities; in the Peasants’ War it shaped male roles based on communal violence; and Anabaptists deployed ‘brother’ and ‘sister’ to radically redefine gender relations. This article will focus on the potential which brotherhood and sisterhood had in encouraging men and women to rethink their gendered identities and express different sensibilities in the German Reformation.