This paper reviews high-quality empirical studies on book reading practices in early childhood that have resulted in increases in child vocabulary. The overarching purpose of this work is twofold: first, to tease apart the myriad ways in which effective book readings can be delivered; and second, to identify questions that remain about book reading and vocabulary learning. We examine various aspects of effective book readings, including the contexts in which the book reading was conducted, the words that were taught through the book reading, the dosage of reading that children received, and the outcome measures used. Findings reveal that six strategies--reading and re-reading texts, explicitly defining words, encouraging dialogue about book-related vocabulary through questions and discussion, re-telling, using props, and engaging children in post-reading activities--are consistently implemented across the studies; however, they are used in widely varying combinations. There is great variability across studies in the number of words taught, the criteria for word selection, and the measures used to assess word learning. Moreover, in many studies, children learn only a small proportion of the number of words taught. Finally, this review identifies critical remaining questions about how to optimize vocabulary learning through book reading that require systematic investigation in order to inform effective practice. (author abstract)