The International Abolitionist Federation (IAF; French: Fédération abolitioniste internationale), founded in Liverpool in 1875, aimed to abolish state regulation of prostitution and fought the international traffic in women in prostitution. It was originally called the British and Continental Federation for the Abolition of Prostitution.

The federation was active in Europe, the Americas, and the European colonies and mandated territories. It felt that state regulations encouraged prostitution while having the effect of enslaving women in prostitution. It felt that the solution lay in moral education, empowerment of women through the right to acquire skills and work, and marriage. The federation experienced opposition from the authorities in Europe and the colonies, who were unwilling to relinquish control, and from reformers who wanted to suppress traffic of women but were less concerned with their welfare. After World War I (1914–18), the IAF was involved in discussions about League of Nations conventions on the issues, and after World War II (1939–45), about United Nations conventions. In later years, the main focus was on eliminating unjust regulations that violated women's rights.

The Regulation System of prostitution in the 19th century typically consisted of policing, brothel licenses, red light districts, registration and forced medical examination of women in prostitution, and forced hospitalization of women in prostitution suffering from sexually transmitted diseases. Abuses included police corruption, registration of underage girls, forced registration of vulnerable women, debt bondage and other ways in which women in brothels were exploited, as well as regulations and other practices that prevented women from leaving prostitution. In the colonies and mandated territories, the regulations were often related to military conquest and control.

The English feminist Josephine Butler (1828–1906), who came from a family involved in the abolition of slavery, believed that forced vaginal examination of women suspected of prostitution violated their basic legal rights. She argued that women lacked sexual autonomy because they were excluded from higher education, professional training, and paid employment and therefore had to choose between marriage or prostitution. Either way, their condition was no different from that of a slave. Butler published many articles on the subject. She toured Europe in 1874 and 1875 to raise support for an international abolitionist movement. In Italy she was able to talk with Giuseppe Mazzini and Giuseppe Garibaldi.

Butler and the pastors and friends who joined her at first campaigned for the "freedom and purity of our English Commonwealth", with which they alluded to the liberty of women and to morality and the family. They were against extra-marital sex but also against celibacy, which they felt leads to depravity. The solution was marriage. In 1882, Butler said, "The best of the restrictions imposed by law is that which encourages and, if necessary, forces citizens of both sexes to practice self-respect."

The abolition campaign rested on two main arguments. The first was "scientific evidence" that state regulation was ineffective and even harmful. The second was that regulation was unacceptable even it were effective in terms of administration and health because it violated human liberty. The abolitionists supported the civil rights of women in prostitution and denied that the state had the right to organize prostitution. Abolitionists were against the abuses inherent in state regulations and against restrictions on the basic freedoms of women in prostitution, such as their right to freedom of movement and to voluntary medical examination. Butler asserted that regulation deprived women of the rights bestowed by Magna Carta and the writ of habeas corpus.

The abolitionists pointed out the double standard of contemporary sexual morality due to which women's bodies were policed and controlled but their male customers were not regulated. They pointed out that this resulted in a double injustice "because it is unjust to punish the sex who are the victims of a vice, and leave unpunished the sex who are the main cause both of its vice and its dreaded consequences". Men both caused prostitution and enforced the system that shamed and punished the women who were its victims. The IAF said, "The social rehabilitation of prostitutes cannot solve the problem of prostitution unless other factors influence the causes of prostitution ... Too often prostitutes are subjected to a disguised form of imprisonment, on the pretext of rehabilitation, in spite of laws which do not state prostitution to be an offence." The IAF felt that treating prostitution as a legal or tolerated institution was "a hygienic mistake, a social injustice, a moral outrage, and a judicial crime".

The abolitionists also thought the trafficking of women would be reduced by the abolition of state-regulated prostitution. They were uneasy about cooperating on measures against the white slave traffic with governments that regulated prostitution because they saw the governments as hypocritical in maintaining a system that created demand for the trafficked women.