This meta-analysis summarized youth, academic, and workplace research on the potential antecedents (demographics, human capital, and relationship attributes), correlates (interaction frequency, relationship length, performance, motivation, and social capital), and consequences (attitudinal, behavioral, career-related, and health-related outcomes) of protégé perceptions of instrumental support, psychosocial support, and relationship quality to the mentor or to the relationship. A total of 173 meta-analytic correlations were computed based on data from 173 samples and a combined N of 40,737. Among antecedents, positive protégé perceptions were most strongly associated with greater similarity in attitudes, values, beliefs, and personality with their mentors (ρ ranged from .38 to .59). Among correlates, protégé perceptions of greater instrumental support (ρ = .35) and relationship quality (ρ = .54) were most strongly associated with social capital while protégé perceptions of greater psychosocial support were most strongly associated with interaction frequency (ρ = .25). Among consequences, protégé perceptions of greater instrumental support (ρ = .36) and relationship quality (ρ = .38) were most strongly associated with situational satisfaction while protégé perceptions of psychosocial support were most highly associated with sense of affiliation (ρ = .41). Comparisons between academic and workplace mentoring generally revealed differences in magnitude, rather than direction, of the obtained effects. The results should be interpreted in light of the methodological limitations (primarily cross-sectional designs and single-source data) and, in some instances, a small number of primary studies.