In keeping with a sociocultural view of children's literacy development, this study investigated the book reading behaviors of African American and Puerto Rican mothers and their Head Start children. Ten African American and 10 Puerto Rican mothers and their children participated. The communicative behaviors of the mothers and children produced during book reading were analyzed and the book reading styles of the dyads were also identified. Results revealed that mothers read the text from the books, responded to their children and asked questions most frequently. The children responded to their mothers' utterances, produced labels/comments, and asked questions most frequently. Puerto Rican mothers produced significantly more labels/comments than did African American mothers. Puerto Rican children had higher assertiveness ratios than their African American counterparts. Four book reading styles were identified in the two groups. Implications for developing interventions that incorporate families' literacy practices are discussed.