Purpose: The authors examined the language used by mothers from low-income and rural environments with their infants at ages 6 and 15 months to identify predictors of maternal language use at the 15-month time point. Method: Maternal language use by 82 mothers with their children was documented during book-sharing interactions within the home in a prospective longitudinal study. The authors analyzed transcripts for maternal language strategies and maternal language productivity. Results: Analyses indicated variability across mothers in their language use and revealed some stability within mothers, as maternal language use at the 6-month time point significantly predicted later maternal language. Mothers who used more language strategies at the 6-month time point were likely to use more of these language strategies at the 15-month time point, even after accounting for maternal education, family income, maternal language productivity, and children's communicative attempts. Conclusions: Mothers' language use with their children was highly predictive of later maternal language use, as early as age 6 months. Children's communication also influenced concurrent maternal language productivity. Thus, programs to enhance maternal language use would need to begin in infancy, promoting varied and increased maternal language use and also encouraging children's communication. (Contains 4 tables.)