The present article provides an analysis of past trends and recent developments in studies of prosocial behavior which began in the latter half of the 1960s. Particular emphasis is placed on studies relating to the subsequent bystander effect, the development of decision-making models incorporating interactions of various factors, empathy, perspective-taking, and prosocial moral judgment as an important mediating factor in motivation, including the viewpoint of self-perception. The article concludes by considering the relevance of studies of prosocial behavior to psychology at large and the directions such studies might take in the future.