This longitudinal study examined the development of mother-infant social toy play in relation to infant language in two samples, one from 11 to 14 months (n = 70), and another from 14 to 17 months (n = 51) infant age. Infants were videotaped during a laboratory free-play session with mothers and were also assessed for language development. Individual variations in mother and infant social toy play behaviors were stable over time, but the frequency of infant initiations and maternal responses increased over time, especially from 11 to 14 months. Maternal responses to infant toy initiations, as well as manipulation and labeling of toys at 11 months were related to infant language at 14 months, while maternal coordinations with infants at 14 months were related to infant language at 17 months. The implications of mother and infant involvement in social toy play are discussed in relation to infant language development.