Despite worldwide efforts to promote HIV Counseling and Testing (HCT), rates of testing remain low. Understanding how high risk groups decide to test and adapting available testing options to their preferences has the potential to broadly improve HCT uptake and cost-effectiveness. This study proposes to use a Discrete Choice Experiment, a survey method increasingly used by health economists for the design of patient-centered health care options, to rigorously quantify HIV testing preferences among two high-risk populations, identify their preferred testing options, and evaluate, in a pragmatic randomized controlled trial (RCT), the effect of a preference-based HIV counseling and testing (PB-HCT) intervention on testing uptake. At a time of heightened focus on health preferences research and patient-centered care, this study evaluates the critical link between preference-based intervention design and efficacy. If the RCT indicates that PB-HCT increases testing rates, the testing options evaluated in this R01 can be offered to high-risk populations in the study area, and the preference elicitation method and tools can be used to inform the design of testing options that better match the preferences of other high-risk populations and in other settings.