The findings from this project have significant public health relevance. The proposed study will a) rigorously characterize the HIV testing preferences of two high-risk populations; b) identify feasible HIV testing interventions that are predicted to increase HCT uptake; and c) identify the effect of a preference-informed HIV testing intervention on rates of testing. More generally, this study evaluates the critical link between an intervention that is systematically designed to match a population's preferences and the efficacy of that intervention. If successful, preference assessments among small samples from key populations could be used widely as an implementation research tool to inform the design of diverse HIV prevention, testing, and treatment interventions; preference-informed interventions, in turn, hold potential to broadly increase intervention uptake and efficacy, both internationally and in the United States.