Commercialized sexuality became a prominent feature of American urban settings in the early 19th century when young men migrated far from the watchful eyes of family as soldiers and laborers. Concentrated in large populations, and unable to afford the comforts of marriage, these men constituted a reliable pool of customers for women who sold sexual access to their bodies. These women turned to prostitution on a casual or steady basis as a survival strategy in a sex segregated labor market that paid women perilously low wages, or in response to family disruptions such as paternal or spousal abandonment. Prostitution could be profitable and it provided some women with a path towards economic independence, although it brought risks of venereal disease, addiction, violence, harassment by law enforcement, and unintended pregnancy. By mid-century most American cities tolerated red-light districts where brothels thrived as part of the urban sporting culture. Fears that white women were being coerced into prostitution led to the “white slavery” scare of the 1910s, spurring a concerted attack on brothels by progressive reformers. These reformers used the emergency of World War I to close public brothels, pushing America’s sex markets into clandestine spaces and empowering pimps’ control over women’s sexual labor. World War II raised concerns about soldiers’ venereal health that prompted the US military to experiment with different schemes for regulating prostitution that had been developed earlier during the Spanish–American War, as well as in the Philippines and Puerto Rico. After the war, the introduction of antibiotics and the celebration of marriage and family nudged prostitution into the margins of society, where women who sold sex were seen as psychologically deviant, yet men who purchased sex were thought to be sexually liberated. The dawning of second-wave feminism gave birth to the sex workers’ rights movement and a new critique of the criminalization of prostitution. Nevertheless, attitudes about prostitution continue to divide activists, and sex workers still bear the brunt of criminalization.