Culturally appropriate, theory-based capacity-building assistance can serve a vital role in helping HIV prevention providers remain up-to-date, effective, and responsive to those they serve. Funded by the Centers for Disease Control and Prevention (CDC), AIDS Project Los Angeles, in collaboration with San Francisco State University's César E. Chávez Institute, conducted full-day site visits and qualitative interviews in 2005 with mid-level management staff of CDC-funded community-based organizations delivering HIV prevention services to Latino communities in the western region of the United States. We found that agencies we visited (1) had not yet adapted the evidence-based interventions they were using at the time of our visit and (2) requested technical assistance and training in the areas of program development, evaluation, group facilitation techniques, consumer recruitment, client retention, intervention adaptation, and materials development. Findings from this needs assessment were used to inform our seven-pronged approach to delivering capacity-building assistance entitled "Acción Mutua" (Shared Action). The approach emphasizes strategic partnerships, stakeholder involvement, organizational self-assessment, culturally appropriate materials development, interactive training, tailored onsite technical assistance, and professional networking opportunities. This article describes our approach in detail, the assessment process we used to develop it, and its implications for capacity-building practice.