BACKGROUND: Sexually transmitted infections (STIs) are spread primarily through sexual contact and are a major cause of morbidity and mortality worldwide. Once identified, some STIs can be cured following appropriate therapy; for others, suppressive regimens and approaches to prevent ongoing transmission are important. The incidence of many common STIs is increasing in the US as well as worldwide, and hundreds of millions of people are currently infected. Laboratory testing plays a major role in the diagnosis and treatment of STIs, and clinical laboratorians should be familiar with the current guidelines and methods for testing. CONTENT: Accurate and sensitive methods to diagnose STIs are essential to direct appropriate antimicrobial therapy and interrupt the cycle of disease transmission. This review summarizes laboratory testing for common bacterial, viral, and parasitic causes of STIs. Disease manifestations reviewed include cervicitis and urethritis, genital ulcerative disease, human immunodeficiency virus, viral hepatitis, human papilloma virus, and vaginitis. Recent advancements in the recognition and management of STIs, including updates to diagnostic algorithms, advances in testing methods, and emerging challenges with antimicrobial resistance, are summarized. SUMMARY: Diagnostic methods and therapeutic guidelines for STIs are rapidly evolving. In combination with changing epidemiology, the development of novel therapeutics, and advancements in diagnostic methods, this has resulted in changing practices in laboratory testing and, subsequently, management of disease. Molecular methods have facilitated personalized therapy and follow-up regimens targeted for individual types or strains of some STIs.