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.