This study examines links between the legalization of marijuana for adults ages 21 or over in Washington State and patterns of marijuana use and related risk behaviors (other drug use, conduct problems, HIV sexual risk behavior) among youth. It also examines links between marijuana legalization for adults and changes in risk factors for youth marijuana use, including youth attitudes; parent marijuana and other drug use and attitudes; parenting practices; perceived peer, sibling, and romantic partner use and attitudes; and marijuana availability. The proposed project is uniquely suited to address these goals. It builds on the Seattle Social Development Project (SSDP) Intergenerational Project (TIP), a study that uses an accelerated longitudinal design, and aims to understand the effects of parent substance use on child development (n = 383 families, 80% living in Washington). TIP includes parents drawn from a prior longitudinal panel study (SSDP), their oldest biological child, and a second caregiver when available. TIP collected recent (2010) pre-legalization data, setting the stage for an evaluation of this important policy shift. Available pre-legalization youth data span ages 1 - 22 and parent data span ages 27 - 35 (2002 - 2010, 7 assessments). The proposed study will add 3 additional annual data collections post-legalization in 2015, 2016, and 2017 with parents, youth, and second caregivers. This study will be one of the first to test links between marijuana legalization for adults and youth marijuana use and related risk behavior. The accelerated longitudinal design will enable the disentangling of development and history (policy change), and will facilitate understanding about the intersection of marijuana legalization and development.