PROJECT SUMMARY This Center strategically addresses a key developmental driver of the youth mental health crisis: Currently, 1 in 5 children has an identified mental health problem as early as age 3. This Mental Health, Earlier (MHE) ALAC- RITY Research Center addresses the grand challenge of achieving population-level impact of early childhood mental health prevention efforts within routine care. The Center targets toddler transdiagnostic behavioral vul- nerability at this pre-clinical phase to impact lifespan mental health. Pediatric primary care is a promising setting for achieving population impact, with broad reach to historically marginalized communities. Taking this to scale requires: (1) systematic incorporation of equity principles across all levels of implementation to ensure equitable adoption and reach of evidence-based interventions across diverse communities and families; and (2) leveraging novel pragmatic and accessible developmentally- and ecologically-based decision and prevention tools feasible for primary care integration. The Center is Northwestern based, including longstanding partnerships with Lurie Children's Hospital, community health centers within AllianceChicago's practice-based research network, and University of Utah Health. The Center's connective thread is an equity-oriented implementation framework, hu- man-centered design methods, and a novel Roll-Out Implementation Optimization trial design, which systemat- ically engages partners in strategy optimization. Center Aims: (1) Develop novel caregiver-focused, system-, and clinician-level strategies to advance equitable implementation of early mental health interventions in pediat- ric primary care; (2) Address the unique needs of diverse communities and families via engagement in culturally attuned, evidence-based prevention services; (3) Create a national resource for equitable implementation of childhood mental health innovation in pediatric primary care, including fostering a cadre of scientific and work- force leaders and experts, and an open access toolkit. Center Signature Project (SP) and Research Projects (RPs) innovate, implement, and integrated evidence-based equitable interventions and strategies, with RPs test- ing novel approaches and/or levels of inquiry designed to address recognized, but understudied, barriers: SP This cluster randomized trial implements an evidence-based toddler mental health risk decision tool with coordi- nated care to the Family Check-Up Online to support parenting and toddler self-regulation; RP1: Deploys digital case-based training to improve clinician confidence and family-centered communication about toddler mental health risk within an anti-racist, culturally grounded framework; RP2: Adapts an evidence-based adjunctive digital single-session intervention to increase families'mental health services use; RP3: Explores unintended conse- quences of early mental health prevention via an integrated bioethical-implementation framewo...