PROJECT SUMMARY/ABSTRACT Multiethnoracial (MER) families have increased dramatically in the U.S., with rates projecting to triple by 2060. The term ?multiethnoracial? describes parental dyads from different racial or ethnic backgrounds (e.g., White- Black, Black-Latinx). Research indicates that MER couples face more stress and family conflict than their monoethnoracial (MoER) counterparts, resulting in increased rates of separation and divorce. To date, no research addresses a key determinant of stress for MER parents, namely the challenge of merging two different racial or ethnic backgrounds, and the resultant stressors that emerge. The early years of parenthood is a period in which MER couples may experience heightened levels of stress because they must merge the values, behaviors, and beliefs of two unique racial or ethnic groups into one family system. Family support is a key resilience factor during this time, buffering the effects of the stress of new parenthood on marital and coparenting conflict, and affecting positive adjustment to this stress. The long-term goal of my research is to identify targets for interventions to reduce stress and improve support for MER families. The specific objective of this proposed research is to identify whether disparities exist in both perceived and biological indicators of stress for MER compared to MoER families, as well as identify modifiable sources of stress, such as low social support, during early parenthood. The central hypothesis is that MER parents will experience greater stress due to racial/ethnic cultural differences, perceived discrimination, and lower access to social supports during early parenthood than their MoER counterparts. Specifically, the proposed research will: (Aim 1) examine if stress in early parenthood differs for parents in MER and MoER dyads, (Aim 2) determine if social support serves as a moderator and/or mediator of the relationship between ethnoracial composition of the couple and stress, and (Aim 3) explore the unique challenges MER families face which contribute to their perceptions of stress, sources of parenting conflict, methods of coping with stress, and the role of social support in these dynamics. The proposed study will employ a sequential explanatory mixed method (SEMM) design with two stages. /Using a nationally representative data set, the first stage of the study will examine links between ethno-racial composition of parent dyads and stress. The second stage of the study will involve qualitative interviews to better understand the quantitative results regarding the factors that contribute to the transmission of stress in MER couples. The outcomes will be theoretically significant by contributing to minority stress theory and broadening its application to MER families while considering the role of support in buffering perceived and biological indices of stress. The findings also have translational significance, by identifying pathways that influence new parents' resilience and susceptibility (e.g., social support) to stress and informing the development of preventive interventions that can contribute to reducing health disparities for MER families.