The current study examined the role of maternal behaviour and toddlers' emotion regulation strategies in the development of children's sustained attention abilities. Participants for this study included 447 children (232 girls) obtained from three different cohorts participating in a larger ongoing longitudinal study. When the children were 2 years of age, mothers brought their children to the laboratory and were videotaped during several tasks designed to elicit emotion regulation and mother-child interaction. Sustained attention was also measured at the same visit via a laboratory task and in a subsequent visit when children were 4.5 years of age. Results indicated that toddlers' use of help-seeking emotion regulation strategies was positively related to sustained attention, while avoidance behaviours and maternal behaviour characterized by high levels of overcontrolling/intrusiveness were negatively related to sustained attention at age 2. Significant interactions emerged such that high levels of maternal warmth/responsiveness buffered the negative associations between low use of distraction and high use of self-comforting emotion regulation strategies and sustained attention at age 2. Maternal behaviour characterized by high levels of warmth/responsiveness also predicted greater growth in sustained attention from age 2 to 4.5. These findings are discussed in terms of how maternal behaviours and children's use of active versus passive emotion regulation strategies relate to sustained attention abilities. (Contains 4 tables and 2 figures.)