Project Abstract In much of eastern and southern Africa, the incidence of HIV and other sexually transmitted infections (STIs) remains high despite the scale-up of promising biomedical and behavioral interventions. Recent studies have documented the crucial role of transactional sex – the exchange of money, material support or goods in age- disparate, sexual relationships – and heavy alcohol use in driving HIV/STI incidence and influencing men's and women's health outcomes. Existing policy responses to this challenge have largely focused on women, with various interventions to reduce women's engagement in transactional sex such as education subsidies, vocational training, and cash transfers for economic empowerment. However, the effectiveness of these interventions has been hindered by the relative lack of programs that target men's behavior. There is a vital need for interventions that can reduce men's engagement in risky behaviors that increase HIV/STI risk. This project will test an innovative, theoretically-motivated economic intervention to reduce men's engagement in transactional sex and other risky behaviors. Leveraging innovations in mobile financial services and research on savings behavior in low-income countries, our intervention will motivate high-risk, income-earning men in Kenya to reduce their spending on risky behaviors and instead save their disposable income in local bank accounts. These bank accounts will include (a) additional incentives to save in the form of lottery-based rewards linked to amounts saved, (b) opportunities to develop savings goals, and (c) periodic reminders about the incentives and goals. Through a direct economic mechanism (incentives to shift expenditures from the present to the future) and a psychological mechanism (increasing future orientation), this intervention can generate significant behavior change and improve health outcomes. We will conduct a randomized controlled trial among high-risk men to determine effects of the savings intervention on their health and economic outcomes. Specific aims of the project are as follows. Aim 1: Determine the impact of the savings intervention on incidence of HIV and other STIs. Aim 2: Determine intervention impacts on savings and expenditures as well as risky health behaviors. Aim 3: Quantitatively and qualitatively assess mechanisms of behavior change among participants and among a sample of female partners. By testing an intervention to promote forward- looking behavior and reduce the risk of acquiring HIV and other STIs in a high HIV/STI burden setting, this project has high potential for scientific and public health impact.