ABSTRACT: We extend current knowledge on prosocial organizing by explaining how membership in organizational categories lead entrepreneurs to reevaluate their ﬁrms’ activities and opportunities. Through a qualitative study of 46 ﬁrms that pursued B Corp certiﬁcation, we developed an identity control model of prosocial opportunity. Our ﬁndings suggest that joining a prosocial category catalyzes identity-driven reﬂexivity, which can alter the ﬁrm’s engagement in prosocial activity. This identity-driven process occurs in tandem with evaluations of opportunity viability and attractiveness, the potential for intra-organizational conﬂict, and the relative power and position that category legitimacy aﬀords the ﬁrm. Our ﬁndings contribute to literature streams on prosocial organizing, identity, and categories.