Abstract Pre-exposure prophylaxis (PrEP) holds great promise to reduce susceptibility to HIV infection for those who are HIV-negative and take PrEP regularly. However, PrEP initiation is serostatus dependent, and starting PrEP when risk emerges requires men who have sex with men (MSM) to maintain regular HIV testing routines and regularly assess PrEP eligibility. Currently many MSM do not test for HIV regularly, and PrEP uptake has been slow. PrEP will not have sufficient impact on HIV incidence among MSM unless it is brought to scale; PrEP coverage of 40-50% would be required to reduce HIV incidence by 25%. Today, PrEP uptake among MSM stands at 8.5%. We propose to test the efficacy of a mobile app (HealthMindr) to promote PrEP uptake in 3 US cities with substantial HIV epidemics among MSM: Atlanta, GA, Jackson, MS, and Washington, DC. The prevention app has already been developed and tested with 121 MSM; 9% of PrEP eligible MSM who used the app initiated PrEP during a 4-month follow-up period. Further, the app was found to be very acceptable to MSM. Minor enhancements to the PrEP component of the app will be made, including addition of additional PrEP information. The app will include components for self-administered risk assessments, developing and supporting a plan for frequent HIV testing, and monthly self-assessment for pre-exposure prophylaxis (PrEP) eligibility. The app will link those eligible for PrEP to services with a locator for PrEP providers, including private providers and details about services available, and with public PrEP navigators. The app will be tested in an RCT versus standard of care (referral to existing PrEP information and resources) in the three cities. The primary outcome will be rate of PrEP initiation, confirmed by tenofovir-diphosphate detection in a dried blood spot (DBS) specimen and/or photographic evidence of PrEP prescription.