--- - |2 There is little understanding about how prosocial behavior toward different targets might change over time, and what might promote initial levels and age‐related changes in prosocial behavior. Thus, this study examined longitudinal change in prosocial behavior toward strangers, friends, and family from early adolescence through the transition to adulthood. Participants included 500 adolescents from the United States (age 12 to age 20; 52% female, 65% European American). Latent growth curve models suggested that prosocial behavior toward strangers increased across early to mid‐adolescence and then flattened out during the transition to adulthood, prosocial behavior toward friends increased steadily, and prosocial behavior toward family was relatively stable across adolescence and then increased. Predictors of initial levels and growth in prosocial behavior varied by target. - Journal of Research on Adolescence, Volume 28, Issue 3, Page 698-710, September 2018.