Academic self-concept describes one’s beliefs in what they can do in a specific academic domain. It is a hierarchical, multidimensional construct that is reciprocally related with achievement. In addition to influencing achievement, academic self-concept predicts students’ motivation including their interest, intrinsic motivation, persistence, and engagement. Academic self-concept is influenced by students’ comparisons to themselves (internal frame of reference) and to others (external frame of reference). Being a member of a homogeneous high-ability peer group is associated with declines in academic self-concept (big-fish-little-pond effect). Academic self-concept is extensively studied using a variety of rigorous methods (i.e., meta-analysis, structural equation modelling, experimental-control design) and has good intercultural generalisability. Due to the role of academic self-concept in students’ achievement and motivational outcomes, educational interventions should take into account mechanisms that foster positive academic self-concept.