Research Findings: The home literacy environment and particularly shared reading are central determinants of children's emergent literacy skills and predictors of their later reading development. Although the importance of frequent shared reading is well established, there is little knowledge about the age at which reading to children starts having beneficial effects. Accordingly, we synthesize five experimental studies (N = 643) to estimate links between retrospectively reported shared-reading onset age, current shared-reading frequency, and a range of emergent literacy skills (expressive and receptive vocabulary, grammatical knowledge, phonological awareness, and oral narrative skill), controlling for child and family characteristics. Retrospective reports of shared-reading onset significantly correlated with current shared-reading frequency and emergent literacy skills. In hierarchical multiple regression analyses, shared-reading onset age predicted grammatical knowledge, receptive and expressive vocabulary, after controlling for child and family characteristics and current shared-reading frequency. However, incremental effects were generally small. Practice or Policy: Findings indicate that early book reading may help to develop emergent literacy skills, even when shared reading begins before the end of children's first year of life. Thus, we encourage parents to engage in frequent, early book reading activities with their children.