Identifying the “prosocial personality” is a classic project in personality psychology. However, personality traits have been elusive predictors of prosocial behavior, with personality-prosociality relations varying widely across sociocultural contexts. We propose the social motives perspective to account for such sociocultural inconsistencies. According to this perspective, a focal quality of agency (e.g., competence, independence, openness) is the motive to swim against the social tide—agentic social contrast. Conversely, a focal quality of communion (e.g., warmth, interdependence, agreeableness) is the motive to swim with the social tide—communal social assimilation. We report two cross-sectional studies. Study 1 (N = 131,562) defined social context at the country level (11 European countries), whereas Study 2 (N = 56,395) defined it at the country level (11 European countries) and the city level (296 cities within these countries). Communion predicted interest in prosocial behavior comparatively strongly in sociocultural contexts where such interest was common and comparatively weakly where such interest was uncommon. Agency predicted interest in prosocial behavior comparatively strongly in sociocultural contexts where such interest was uncommon and comparatively weakly where such interest was common. The results supported the social motives perspective. Also, the findings help to reestablish the importance of personality for understanding prosociality.