This study investigated the relations among parenting, coparenting, and effortful control in preschoolers. The sample included 89 families with 2 parents and their firstborn 36-month-old children. Information was obtained by means of observation and parent-report questionnaires. In general, maternal parenting, paternal parenting, and coparenting were related to effortful control. Effortful control was more strongly predicted from parenting and coparenting when the same measurement method (observation or parent reports) was used. For both observation and parent reports, coparenting contributed to effortful control over and above maternal and paternal parenting. The results indicate the importance of adding indicators of triadic family processes to the study of parenting and young children's effortful control.