LYNX: A Novel Mobile App to Support Linkage to HIV/STI Testing PrEP for Young Men Who Have Sex With Men

Inclusion Criteria: * No HIV test in the past 3 months (self-reported). * Not known to be HIV-infected (self-reported). * Not currently taking PrEP (self-reported). * Owns an Apple operating system (iOS) or Android mobile phone and willing and able to download the LYNX app onto their phone. * Willing and able to attend an in-person baseline visit in the Tampa or Chicago area. * Able to understand, read, and speak English. * Participants ages 15-18: self-report at least one episode of anal intercourse with a male or transfemale partner during the last 6 months * Participants ages 19-24: self-report evidence of high risk for acquiring HIV infection including at least one of the following: 1. at least one episode of condomless anal sex with an HIV-positive or unknown HIV status male or transfemale partner during the last 6 months; or 2. Anal sex with 2 or more male and/or transfemale partners during the last 6 months; or 3. Exchange of money, gifts, shelter, or drugs for anal sex with a male or transfemale partner during the last 6 months; or 4. Sex with a male or transfemale partner and has had an STI during the last 6 months. Exclusion Criteria: * Currently enrolled in another HIV intervention study * Prior enrollment in an HIV vaccine trial with receipt of experimental vaccine product * Enrollment in an earlier phase of LYNX study * Any medical, psychiatric, or social condition or other responsibilities that, in the judgment of the investigator, would make participation in the study unsafe, complicate interpretation of study outcome data, or otherwise interfere with achieving the study objectives.