The positive effects of joint book reading (JBR) between parents and children have been widely presumed. However, the impact of JBR has not been widely investigated in toddlers, nor has the extant literature considered the context of JBR reading sessions (e.g., reader, prompt, occasion, who chose the book, etc.). The present study examined the occurrence of JBR in middle-class homes, using two methodologies (i.e., questionnaire and daily journal), and then examined variables derived from these methods with children's vocabulary, as assessed by the MacArthur-Bates Communicative Development Inventory. Indicants of the frequency of dBR and the variety of titles read were strongly correlated with vocabulary outcomes, especially expressive vocabulary. In addition, dBR was determined to occur in two independent contextual situations: one that occurred as a matter of regular routine, and another that occurred more irregularly and spontaneously; the former was marginally associated with receptive vocabulary, while both factors contributed significantly and independently to the prediction of expressive vocabulary. These findings are in accord with the hypothesis that JBR promotes language skills, and extends them to toddlers. (Contains 1 figure and 5 tables.)