Abstract Compared to adolescents or adults in mid-life, young adults are at higher risk of death and disease from a variety of causes, most of which are preventable, such as mental health problems, substance use, sexually transmitted infections, homicides, and motor vehicle accidents. Although early adulthood is an important period to understand, little research has focused on cross-cultural heterogeneity in potential risk and protective factors during early adulthood. The proposed research builds on the ongoing Parenting Across Cultures longitudinal study that began in 2008 with recruitment of a sample of 1,417 8-year-old children and their mothers and fathers from 9 countries (China, Colombia, Italy, Jordan, Kenya, Philippines, Sweden, Thailand, and the United States). We have since assessed families annually through interviews with children, mothers, and fathers about the parent-child relationship, the child’s adjustment, attitudes and beliefs, and cultural values, with 90% retention of the original sample. During the next project period, the original child participants will be 22 to 26 years old, providing an unprecedented opportunity to understand how childhood and adolescent experiences in the most diverse long-term longitudinal study ever conducted culminate in adjustment during early adulthood. We will conduct interviews annually with young adults and their parents to assess family and cultural influences on decisions, risks, competencies, and opportunities during this developmental period that is characterized by major health risks and transitions in education, work, residential status, intimate partnerships, and parenthood. We address three aims: (1) We will build a developmental model of young adult adjustment and maladjustment using mediators and moderators at the individual, family, and culture levels, including potential risk and protective factors. (2) We will examine predictors of parent-young adult relationships across cultures that normatively differ in how changes in family relationships are experienced and negotiated in early adulthood. (3) We will examine the impact of COVID-related disruptions in education, work, and other important domains on subsequent adjustment. We have collected data on COVID-related experiences every 3 months since the start of the pandemic, situating us well to be able to examine these experiences in relation to adjustment in the aftermath of the pandemic. Addressing these aims in the most diverse, prospectively studied, multi-national sample to date will have major public health implications in informing scientific understanding of predictors of adjustment during early adulthood, a developmental period characterized by high morbidity and mortality due to mental health problems, substance use, and other largely preventable causes, as well as opportunities for positive adaptation. This work will inform programming and policy to improve population health and well-being by identifying novel targets for p...