PROJECT SUMMARY/ABSTRACT The majority of children on the autism spectrum have a co-occurring mental health disorder and emotion dysregulation is posited to serve as a risk factor for the development of mental health disorders. However, regulating emotions is a dynamic process that is influenced by the interplay of child characteristics and the family context and there is a paucity of research examining these processes in children on the autism spectrum. The long-term goal is to reduce the co-occurrence of mental health disorders in children on the autism spectrum. The overall objective in this application is to clarify the associations between the family context and children’s development of emotion regulation. The central hypothesis is that the strength and direction of the associations between the family context and emotion regulation depend upon children’s characteristics, including autism diagnostic status and the heterogeneity of autism symptom severity. The rationale for the proposed research is that once we identify contextual factors associated with emotion regulation, and for whom they are applicable to, then we can develop appropriate interventions to reduce the development of co-occurring mental health disorders. The central hypothesis will be tested by pursuing two specific aims: 1) Identify whether dynamics of emotion regulation differ for children on the autism spectrum compared to non-ASD children and whether, among children on the autism spectrum, such dynamics vary as a function of child characteristics; and 2) Identify the extent to which aspects of the family context, previously identified in NT children, are associated with emotion regulation and whether child characteristics moderate these associations. The PI’s preliminary studies indicate strong feasibility of recruiting a sample of young children on the autism spectrum and measuring emotion regulation. The proposed research will include 220 children (110 ASD; 110 non-ASD) and their parents. The proposed research is innovative, in the applicant’s opinion, because it represents a substantive departure from the status quo by using a multi-method design to understanding the dynamics of emotion regulation in children on the autism spectrum and identifying which children are most at risk for difficulties regulating emotions. The proposed research is significant because it is expected to inform efforts to promote healthy emotional development in children on the autism spectrum.