Bacterial sexually transmitted infections (STIs) have been increasing over the past 2 decades in gay, bisexual, and other men who have sex with men. With the widespread use of early human immunodeficiency virus (HIV) treatment, which virtually eliminates transmission risk, and the availability of HIV pre-exposure prophylaxis, there have been attitudinal changes regarding HIV infection with resultant increases in sexual contact and declines in condom use. Doxycycline is used for primary prophylaxis in a number of infectious diseases. We conducted a state-of-the-art review to examine the current state of research, knowledge gaps, and challenges around the use of doxycycline prophylaxis to prevent syphilis and other STIs. International academic and government experts met in March 2019 to frame the initial inquiry, which was supplemented by focused literature searches. Two small short-term randomized controlled trials examining doxycycline prophylaxis found high efficacy. Five additional clinical studies are underway or in development. Studies differed in design, population, outcomes, and safety measures. Doxycycline prophylaxis for bacterial STIs shows promise. Better and more robust data are needed on efficacy; target population; community acceptability; behavioral risk compensation; doxycycline dose, regimen, and formulation; long-term safety; antimicrobial resistance; cost-effectiveness; and risk–benefit.