Over 34% of adolescents are overweight or obese. Observational research suggests that family behaviors, such as family meals or parental role modeling, may play an important role in shaping adolescent behaviors and resulting weight status. However, results are not consistent across studies. Family systems theory asserts that family behaviors must be understood within the global family context. Global family factors, such as parent-child relationship quality or general family functioning, influence how family behaviors are experienced by the adolescents. Thus these factors may be potentially powerful modifiers of the associations between family behaviors and adolescent outcomes. Omitting the family context within which these family behaviors occur may explain the inconsistent research findings. We propose to address this fundamental gap by conducting a large cohort study to determine how specific global family factors influence associations between family behaviors and adolescent weight-related outcomes. The overall objective of this proposal is to examine independent and interactive associations of family behaviors and global family factors with adolescent weight and with weight-related behaviors. To achieve this objective, we will use longitudinal repeated measures data and newly collected survey data from the Growing Up Today Study 2 (GUTS2), an ongoing cohort study of adolescents. We will link adolescents' data to data from their mothers, who are participants in the Nurses' Health Study 2. The proposed study's large size (n=10,442), prospective design, basis in sound behavior theory, and multi-level data on mothers and adolescents provide an unsurpassed opportunity to study the influence of the family context on adolescent weight and weight-related behaviors. Results of this study will provide a much-needed basis for effective family-based obesity prevention interventions.