Sexually transmitted infections (STIs) have an interesting history and are believed to have existed since earliest times. Their transmission is related to human nature and frailties and they can have devastating effects on the body, on the mind and psyche, and on the ability to procreate. Perceptions about STIs have varied from one society to another and even today, for example, the industrialized world has a relatively enlightened approach to human immunodeficiency virus (HIV) infection, whereas some southern African countries have, at one point, virtually denied their existence. The recent history of STIs mirrors, to a degree, the development of modern scientific medicine. The advent of microscopy in the late 19th century allowed the identification of the causative organism of gonorrhea and, in the early 20th century, the causative organisms of chancroid and syphilis were identified. The first serological test for any infection, the Wasserman reaction, helped to confirm the presence of syphilis and the first disease-specific modern treatment for an infection, arsphenamine, was developed for syphilis in 1909. Discovery of the bacteriostatic sulfonamides in 1937 by Domagk permitted the first effective treatment for gonorrhea but antimicrobial resistance soon occurred. With manufacture of penicillin, the first bactericidal antibiotic in 1943, both gonorrhea and syphilis became reliably treatable. Resistance to antibiotics, now perceived as a major threat with bacterial infections, has not spared Neisseria gonorrhoeae and chromosomal and plasmid-mediated resistance have been identified. As the science of virology developed in the middle 20th century, other common STIs became more readily recognized, such as genital warts caused by strains of the human papillomavirus (HPV) and genital herpes caused by the herpes simplex virus (HSV). Indeed, the first reliable antiviral agent, acyclovir, was developed to treat genital and oral herpes simplex lesions in the early 1980s. Meanwhile, the science of immunology was developing in the latter half of the 20th century, retroviruses had just been discovered and, in 1983, HIV was identified as the cause of acquired immune deficiency syndrome (AIDS). The immunological basis of this most