PROJECT SUMMARY Young persons, aged 13-24 years, accounted for 21% of new infections in the United States in 2018, and 81% of these occurred in young gay, bisexual, and other men who have sex with men (YGBMSM). Currently, there are 4 different regimens of pre-exposure prophylaxis (PrEP) available for YGBMSM: 1) daily tenofovir disoproxil fumarate co-formulated with emtricitabine (TDF/FTC), 2) daily tenofovir alafenamide co-formulated with emtricitabine (TAF/FTC), 3) peri-coital TDF/FTC (“2-1-1 PrEP”), and 4) injectable long-acting cabotegravir. PrEP Choice is a package of three mobile health tools designed to increase the uptake and adherence to PrEP for YGBMSM, aged 13-24 years, to be tested in multiple sites in the United States. PrEP Choice consists of 1) MyPrEP, a website to help YGBMSM choose the type of PrEP that works best for them; 2) PrEPmate, a two- way SMS texting tool to check in with YGBMSM on a weekly basis and troubleshoot any problems with PrEP that arise; and 3) PrEPsmart, an app that reminds PrEP users taking PrEP pills when their next pill should be taken. These tools have been developed and tested individually; this is the first study to test the package of these tools to see if they increase the proportion of YGBMSM who take PrEP, and their adherence to PrEP once they start. The study begins by ensuring that PrEP Choice is relevant for both Spanish- and English- speaking YGBMSM across the country, through the use of focus groups, followed by a technical pilot in 20 YGBMSM, to work out any bugs in the system and to help determine how best to apply PrEP Choice in this population. Then, 200 YGBMSM not currently on PrEP will be recruited into a trial in which 100 are randomly chosen to get PrEP Choice, and the other 100 are randomly chosen to get a brochure describing the different types of PrEP available. After 9 months of follow-up, PrEP starts and use over time will be compared between the two groups. Then, the 100 participants initially given the brochure only will get access to the PrEP Choice package, and both groups will be followed for another 9 months to study their use of PrEP over time. PrEP use will be measured by testing for tenofovir diphosphate (TFV-DP) levels in dried blood spots (for the 3 types of PrEP that use pills) or the number of PrEP injections they get (for injectable long acting cabotegravir.) The primary outcome is PrEP use at 9 months into the study, and this study will enroll enough participants to be able to tell whether there is at least a 20% increase in the proportion of YGBMSM who use any PrEP in the PrEP Choice group compared with the brochure group, and a 22.5% increase in PrEP adherence (as measured by TFV-DP levels or administration of long-acting cabotegravir) in the PrEP Choice group compared with the brochure group. The cost and cost-effectiveness of the PrEP Choice package will also be assessed for YGBMSM. The trial will be conducted through the Adolescent Trials Network for HIV/AIDS Interventions (ATN), making use of their biostatistical and modeling resources, geographic and site diversity, and multidisciplinary expertise, including young advisors from the target population.