The goal of this project is to study implementation of Eban II, an evidence-based risk reduction intervention for couples. Using a hybrid implementation/effectiveness design, this study will investigate: (1) processes and determinants of implementation in 10 community-based organizations (CBOs) in California, and (2) real-world effectiveness of the intervention as it is delivered to 180 couples. The study is guided by organizational change theory as conceptualized in the Texas Christian University Program Change Model, a model of phased change from exposure to adoption, implementation, and sustainability. Implementation will be supported by a number of strategies and tools. Our primary implementation aims are: (1) to assist 10 CBOs to implement and sustain an evidence-based intervention for HIV serodiscordant African American couples; specifically, to partner with CBOs to expose providers to the intervention, facilitate its adoption and implementation, and sustain practice; and (2) to evaluate processes and determinants of implementation and effectiveness; specifically, to assess acceptability of the intervention, and barriers and facilitators to its implementation; examine key determinants of fidelity; understand how the project’s implementation strategies and tools affect adoption, fidelity, and effectiveness; and examine key determinants of sustainability. Our primary effectiveness aim is to evaluate the effect of intervention implementation on participant outcomes, specifically incidents of protected sex and proportion of condom use. We also have a secondary aim to determine the cost-effectiveness of implementation of Eban II, as measured by implementation costs and potential cost savings associated with a couples-based intervention. To achieve these aims, implementation will be studied with a mixed methods evaluation. At the agency level, 200 staff members will complete measures of organizational context and climate, and 50 of those individuals (key stakeholders) will be interviewed periodically throughout implementation. Effectiveness of Eban II will be assessed using a randomized delayed enrollment (waitlist [WL]) control design to evaluate the impact of treatment on outcomes at posttest and 3-month follow-up. We will use multi-level hierarchical modeling with a multi-level nested structure to evaluate the effects of agencyand couples-level characteristics on couples-level outcomes (e.g., condom use). Thirty-four individuals will be trained as site coordinators, facilitators, and data collectors, retaining CBO staff wherever possible. This study will produce important information regarding the value of this model and model-guided implementation tools and strategies for use in implementing Eban II and other evidence-based programs in diverse treatment settings. Accordingly, the fields of HIV prevention research, community-based participatory research, and implementation research will all be informed by the study findings.