Self-efficacy has been found to be an important predictor of various learning-related outcomes. In this chapter, we focus on the role of academic self-efficacy in the context of reading among school-aged children. We first discuss measurement of reading self-efficacy both theoretically and in the light of recent empirical findings. We then turn on reviewing how reading self-efficacy contributes to reading achievement and development and focus on the variations in this relationship. Recent findings on how reading self-efficacy changes and develops over time as well as the varying role of the four theorized sources of self-efficacy in this development are being discussed. Finally, we look more closely on how reading self-efficacy can be intervened as a part of reading support by explicitly targeting the four sources of self-efficacy. The chapter concludes with suggestions for future research on children’s academic self-efficacy in reading. Increased understanding of the individual processes in reading self-efficacy development seems to be needed to better address the needs of different groups of students with differentiated instruction.