This paper examines factors influencing prosocial intentions. On the basis of the norm activation model (NAM), we propose that four variables influence prosocial intentions or behaviours: (1) personal norms (PN), reflecting feelings of moral obligation to engage in prosocial behaviour, (2) awareness of adverse consequences of not acting prosocially, (3) ascription of responsibility for the negative consequences of not acting prosocially, and (4) perceived control over the problems. We conducted a series of experimental studies to examine how the NAM variables are causally related. As hypothesized, problem awareness, responsibility, and outcome efficacy played an important role in the development of PN and various types of prosocial intentions in the social as well as environmental domain.