Millions of individuals donate their time to volunteer work each year. Additionally, expectations of socially responsible practices on the part of organizations and the positive relationship between the social and financial performance of organizations are leading to a growing interest in corporate social responsibility among management and researchers. One method to achieving greater corporate social responsibility is corporate-sponsored volunteering. Many benefits have been associated with corporate volunteerism. However, an understanding of why these outcomes occur is lacking. Also lacking is an understanding of why individuals engage in corporate volunteerism. Although studies have identified several demographic variables associated with volunteering in general, few studies have examined variables beyond simple demographics, and fewer still have examined antecedents of corporate volunteering. In the current study, the theory of planned behavior, functional motives for volunteering and citizenship performance, and perceived locus of causality are used to integrate contextual, attitudinal, situational, and motivational variables in order to present and empirically test a framework to help explain why individuals participate in corporate volunteerism. Data were collected from 110 individuals employed in two organizations supporting corporate volunteerism in order to examine the antecedents of participation in this behavior. Results indicated that antecedents of intentions included in the theory of planned behavior and its extensions were related to intentions to participate in corporate volunteerism and, in some cases, actual participation in this behavior. Furthermore, functional motives for volunteering and citizenship performance were related to the regulations specified by the perceived locus of causality continuum. These motives, conceptualized as general orientations towards particular behaviors relevant to a contextual domain, were related to the situation-level decision-making antecedents of intentions in several cases. Finally, several of the relationships between the contextual-level generalized motivational constructs and intentions to participate in corporate volunteerism were mediated by the situational-level antecedents of the theory of planned behavior. Specifically, the relationship between social motives and intentions was mediated by subjective norms. The relationships between each of identified regulation, values, understanding, and organizational concern motives with intentions were mediated by attitudes toward corporate volunteerism. Perceived behavioral control also mediated the relationship between understanding motives and intentions.