Individual and shared intentions to participate in a group activity were studied for Koreans and for Americans. For Koreans, individual intentions were functions of attitudes, whereas shared intentions were functions of social identity reactions (i.e., self-categorization, affective commitment, and evaluative significance). For Americans, individual intentions were functions of attitudes and group norms (i.e., internalization), while shared intentions were functions of subjective norms (i.e., compliance) and group norms. The differential effects of personal and social factors on intentions were explained from the viewpoint of social influence theory. Further, cultural background (i.e., an independent-based versus an interdependent-based orientation) was found to moderate these effects.