Prostitution was well-established and widespread in Medieval Europe. "Easy women" could be procured in the countryside and in most urban centers, at fairs and weddings, in brothels, in public baths, and on street corners. Countless laws, ordinances, and regulations governing the practice of prostitution stand as proof of its ubiquity. There were public and private prostitutes, streetwalkers and cloistered prostitutes. Some plied their trade in a single location for their entire careers; others moved from village to village, following caravans of merchants or going from fair to fair.
Women became prostitutes in a variety of ways. In one study of prostitutes in Dijon between 1440 and 1540, out of 77 cases, only 11 entered the profession by choice. Of the remaining women, some were prostituted by relatives or godparents. Poverty drove many women to prostitution, as did family conflict and estrangement. A woman who was disgraced for one reason or another might find prostitution to be the only means available for her to make a living. Twenty-one women in the Dijon study were forced to become prostitutes after being disgraced by rape. In some locales, simply pulling a woman's headcovering off of her head was enough to declare her a whore.
Prostitutes didn't age well, and once they were in their thirties, they had to find another way to make money. Some continued in the trade, becoming madams of brothels or managers of bathhouses. A few reformed and became nuns or entered institutions for repentant prostitutes. Others fell into extreme poverty and a life of transience, begging and stealing for a living. But the most common way for a prostitute to move on with her life was to marry. Thirty-ish prostitutes were still young enough to be marriageable, and prostitution did not carry the same stigma then as it does today in most of the world. Oftentimes, local charities would even raise a dowry for a prostitute.
Restrictions on prostitution varied widely by location, but a few common threads exist. Prostitutes could not work during Lent or during mass. They had to wear some outer sign of their trade; sometimes this simply meant not wearing the coif that distinguished respectable women from whores, and sometimes it meant wearing a kind of sash. Only unmarried men and men "of age" could legally use the services of a prostitute, although you can be sure there were exceptions. Interestingly, in some places, one prostitute could entertain several men at once, but one man could not have more than one prostitute at once. The most common restriction on prostitutes was that of geography. Cities and towns tried to restrict the practice of prostitution to certain areas; in London, for example, prostitutes had to stay in bathhouses on the "other side" of the Thames (the south side, to which all disreputable people were restricted.)
Prostitution, while more or less looked down upon by the powers that were, was tolerated as a necessary evil. While it is true that public ordinances restricted the practice of selling sex, the very existence of the ordinances points to one important fact: prostitution was legal. On occasion, in the midst of war or pestilence, or after a particularly stirring sermon from a zealous priest, some towns did attempt to drive out the prostitutes, but the results were temporary at best. In December 1254, Saint Louis ordered the expulsion of all "women of evil life" from France, and he repeated the order in 1256. His protests were in vain, however, as the practice continued to thrive and his orders were largely ignored. Saint Augustine himself wrote, "Remove prostitutes from human affairs, and you will unsettle everything on the account of lusts." That seems to sum up the Medieval view of prostitution.
This unconcerned public stance on prostitution can perhaps be attributed, surprisingly, to religion. In the theology of the day, fornication was divided into a whole spectrum of sinfulness. A married woman who committed adultery was an abomination. A married man who had sex with a woman other than his wife was sinful, but not as sinful as the woman. Society, on the whole, accepted that unmarried men "needed" to have sex, and prostitution was the least sinful way for their needs to be fulfilled. Prostitutes of the day did not seem to be unusually concerned for their immortal souls. They went to mass regularly and gave their confessions. The Catholic Church in those days was far more concerned with spiritual sins than with sins of the flesh. Durand de Saint-Pourçain wrote in his "Commentary on Sentences" that "in natural law simple fornication constitutes only a venial sin." In other words, it wasn't a major transgression for two unmarried people to have sex (as long as one was a woman and one was a man, but that's another node.)
For more information, check out: Women's Lives in Medieval Europe: A Sourcebook, edited by Emilie Amt; La Prostituzione Nel Medioevo, by Jacques Rossiaud; and Meanings of Sex Difference in the Middle Ages, by Joan Cadden.