Two studies examined the discriminant and incremental validity of self-concept and academic self-efficacy. Study 1, which meta-analysed 64 studies comprising 74 independent samples (N = 24,773), found a strong mean correlation of 0.43 between self-concept and academic self-efficacy. The domains of self-concept and self-efficacy, and the domain matching between them, moderate the strength of the correlation between self-concept and academic self-efficacy. Global self-concept was associated with weaker correlations than were academic and subject-specific self-concept. Academic self-efficacy had higher incremental validity than self-concept. Study 2, which examined data-sets from Programme for International Student Assessment 2000, 2003 and 2006, found that the mean correlation ranged from 0.31 to 54. Self-concept sometimes had higher incremental validity than academic self-efficacy. The higher incremental validity of self-concept may result from the wording and domain of self-concept measure as well as specificity matching between self-concept and academic achievement. (Contains 7 tables.)