This prospective longitudinal study examined the contribution of dimensions of maternal responsiveness (descriptions, play, imitations) to the timing of five milestones in children's (N= 40) early expressive language: first imitations, first words, 50 words in expressive language, combinatorial speech, and the use of language to talk about the past. Events-History Analysis, a statistical technique that estimates the extent to which predictors influence the timing of events, was used. At 9 and 13 months, maternal responsiveness and children's activities (e.g., vocalizations, play) were coded from videotaped interactions of mother – child free play; information about children's language acquisition was obtained through biweekly interviews with mothers from 9 through 21 months. Maternal responsiveness at both ages predicted the timing of children's achieving language milestones over and above children's observed behaviors. Responsiveness at 13 months was a stronger predictor of the timing of language milestones than was responsiveness at 9 months, and certain dimensions of responsiveness were more predictive than others. The multidimensional nature of maternal responsiveness and specificity in mother – child language relations are discussed.