Electronic books (e-books) are a prevalent method for integrating technology in preschool and elementary classrooms; however, there is a lack of consensus concerning the extent to which e-books increase literacy skills in the domains of comprehension and decoding. This article assesses the efficacy of e-books with a comprehensive review method, including a systematic literature search, comparison of outcomes with effect sizes, and discussion of individual studies that met either (a) randomized-trial synthesis criteria, or (b) quasi-experimental/observational narrative synthesis criteria. Seven studies met the randomized-trial criteria and 20 studies met the quasi-experimental/observational narrative review criteria. Results from the randomized trials indicate that the effects of e-books on comprehension-related outcomes were small to medium in size. Only two randomized trials examined decoding-related outcomes, thereby preventing firm conclusions. The narrative review suggests some interactive e-book features support comprehension, whereas other incongruent features may hinder comprehension. Educational implications and future research directions are discussed. (author abstract)