Theorists have long assumed that people's self-esteem and social relationships influence each other. However, the empirical evidence has been inconsistent, creating substantial uncertainty about whether relationships are in fact an influential factor in self-esteem development and vice versa. This meta-analysis synthesizes the available longitudinal data on the prospective effect of social relationships on self-esteem (48 samples including 46,231 participants) and the prospective effect of self-esteem on social relationships (35 samples including 21,995 participants). All effects controlled for prior levels of the outcomes. Results showed that relationships and self-esteem reciprocally predict each other over time with similar effect sizes (β = .08 in both directions). Moderator analyses suggested that the effects held across sample characteristics such as mean age, gender, ethnicity, and time lag between assessments, except for the self-esteem effect on relationships, which was moderated by type of relationship partner (stronger for general relationships than for specific partners) and relationship reporter (stronger for self-reported than for informant-reported relationship characteristics). The findings support assumptions of classic and contemporary theories on the influence of social relationships on self-esteem and on the consequences of self-esteem for the relationship domain. In sum, the findings suggest that the link between people's social relationships and their level of self-esteem is truly reciprocal in all developmental stages across the life span, reflecting a positive feedback loop between the constructs. (PsycInfo Database Record (c) 2021 APA, all rights reserved).