Latinx people are the largest and fastest growing minority population in the U.S., yet most lack access to community responsive preventative interventions to reduce substance use among youth. Effective implementation of evidence-based interventions that can be delivered online is critical to reduce substance use and problem behaviors among ethnic populations and to scale up for broad dissemination. Adaptation to address community needs has improved parenting practices and youth outcomes beyond the original evidence-based parenting interventions, and adapted parenting programs have the potential to improve cultural socialization, which is associated with improved behavioral outcomes among Latinx youth. However, ongoing tensions in the field highlight the question of whether deep adaptations compared to surface-level adaptations (e.g., translation only) are needed. The FCU is an evidence-based parenting program that has a strong history of reducing substance abuse and externalizing symptoms (e.g., problem behaviors). A community-based participatory approach will be employed to culturally adapt the FCU Online and identify implementation strategies to improve access to and adoption of the intervention, leveraging community and resiliency-promoting assets. Promotores de salud, Spanish-speaking community health workers in an existing community-based research network will deliver the program. To reach the goals of the study, the following aims will guide this research. In Aim 1, a community advisory board of 6 parents and 6 promotores de salud will meet monthly to guide the ecological adaptation of the FCU Online modules and implementation strategies with promotores. In Aim 2, the online version of the intervention will be adapted using iterative Plan-Do-Study-Act cycles to get usability feedback from members of the community advisory board, consistent with best practices designed to adapt interventions in community settings. In Aim 3, using a Hybrid 1, mixed methods design, researchers will assess feasibility, accessibility, adoption, and potential effectiveness of the adapted intervention, FCU-L Online. The team will recruit 108 Latinx families into a 3-arm wait-list randomized control trial: n=36 in the culturally adapted FCU-L Online (e.g., deep adaptation), n=36 in the FCU Online in Spanish without adaptation (e.g., surface level adaptation), and n= 36 in a waitlist control group. Feasibility, accessibility, and adoption will be assessed according to quantitative benchmarks, and qualitative feedback will assess the barriers and facilitators of implementation. Potential effectiveness will be assessed (p \< .15), including improvement of key intervention mechanisms (parenting practices, parenting efficacy, and cultural socialization) as well as child outcomes (substance use, intentions to use, and externalizing behavior). Findings from this study will inform a Hybrid II randomized controlled implementation trial to test effectiveness while scaling up dissemination of the FCU-L Online. This research could ultimately reduce lifetime risk for substance use among Latinx youth by improving parenting practices and supporting cultural socialization.