Well-established psychological theories indicate that interpersonal relationships and emotional well-being are linked in fundamental ways (Coyne, 1976; Sullivan, 1953). Indeed, difficulties in close relationships can contribute to emotional adjustment problems, and emotional problems can adversely affect close relationships. Moreover, different close relationships are especially significant in terms of development and adjustment at different stages of the life span. The current review focuses on childhood and adolescence, developmental stages at which friendships are particularly important. This article presents the results of 16 meta-analyses including 589 unique effects from 233 studies that examine concurrent and longitudinal associations between youths' friendship experiences (number of friends, positive friendship quality, negative friendship quality) and their emotional adjustment (depressive symptoms and loneliness). Studies examining these associations are mixed in regard to whether significant effects emerge. The current research synthesis provides more stable estimates of the effects. In fact, relatively small but significant concurrent and longitudinal associations emerged between the 3 indices of friendship with depressive symptoms and loneliness. The results also suggest that friendship experiences may be more closely linked with loneliness than depressive symptoms and that negative friendship quality may be related to friendship experiences more strongly than number of friends or positive friendship quality. Interestingly, some of the relations were found to be stronger for younger youth. Implications for prevention and intervention efforts are discussed. (PsycInfo Database Record (c) 2020 APA, all rights reserved).