PROJECT SUMMARY Successfully reaching and enrolling fully representative target populations in public health interventions is a highly desired, but notoriously difficult, prospect, especially when an initiative is focused on socially charged issues or health conditions that affect vulnerable subgroups. For example, HIV/AIDS has disproportionately high morbidity among a number of minority/marginalized populations, and faces a stigma that further complicates recruitment efforts. The commercial sector, on the other hand, faces similar challenges for engaging diverse audiences, but has achieved highly notable successes in its marketing and advertising efforts. Brands and companies have effectively utilized a number of innovative approaches to increase operational efficiency, measure campaign effectiveness, and capture relevant data to pinpoint specific consumer behavior. A comparable approach, tailored to meet the idiosyncratic needs of the public health enterprise, would offer significant improvement to its ability to engage with intended audiences. Those proven methods, however, entail significant capital and dedicated personnel that are not typically available to the majority of public health organizations. Thus, there is a pronounced yet unmet need for more scalable toolsets that can improve outreach and engagement of target populations. In order to address these challenges, this project seeks to increase representative enrollment through customized outreach analyses and informed tailoring of recruitment and engagement strategies. The proposed web-based system will enable researchers to conduct typology stratification of participant groups based on demographic, psychographic, and other pertinent characteristics, and will provide a platform for iterative improvement toward encouraging desired enrollee behavior in real-time. This targeted approach holds the promise to enhance participant engagement in public health interventions, and will be tested in the context of facilitating enrollment in an eHealth study targeting HIV+ men who have sex with men (MSM).