The present study examined correlates of mastery-related behavior across the infant's second year of life. Maternal control style was quantified on a control to support-of-autonomy continuum, infant-mother attachment was assessed in the Strange Situation, and mastery-related behavior was observed in a toy play session at 12 and 20 months. Infants whose mothers were supportive of their autonomy displayed greater task-oriented persistence and competence during play than did infants of more controlling mothers; securely attached and avoidant infants tended to exhibit greater persistence at tasks than anxious-ambivalent babies, and ambivalent babies were the most negative in affect.