In a 19-year longitudinal study, childhood personality characteristics (assessed by teachers at ages 4 to 6) were significantly related to both initial levels and changes in parental judgments of shyness and aggressiveness. Long-term stability was demonstrated by the fact that overcontrollers had consistently higher scores in shyness and undercontrollers in aggressiveness. However, undercontrollers' shyness and overcontrollers' aggressiveness changed over time from a low to a high level. Also, both types assumed adult social roles, such as leaving the parental home, establishing a first romantic relationship, and getting a part-time job, at a later time than the resilient participants. A mediation analysis indicated that under-and overcontrollers' increasing aggressiveness between age 17 and 23 was due to their longer latency of getting a part-time job. Together, results demonstrate the importance of considering person-environment transactions in explaining both change and stability in personality between childhood and adulthood.Findings from a number of longitudinal studies have shown that childhood personality predicts important life outcomes in Correspondence concerning this article may be sent to: Jaap Denissen,