Sex trafficking is human trafficking for the purpose of sexual exploitation. Perpetrators of the crime are called sex traffickers or pimps—people who manipulate victims to engage in various forms of commercial sex with paying customers. Sex traffickers use force, fraud, and coercion as they recruit, transport, and provide their victims as prostitutes. Sometimes victims are brought into a situation of dependency on their trafficker(s), financially or emotionally. Every aspect of sex trafficking is considered a crime, from acquisition to transportation and exploitation of victims. This includes any sexual exploitation of adults or minors, including child sex tourism (CST) and domestic minor sex trafficking (DMST). It has been called a form of modern slavery because of the way victims are forced into sexual acts non-consensually, in a form of sexual slavery.

In 2012, the International Labour Organization (ILO) reported 20.9 million people were subjected to forced labor, and 22% (4.5 million) were victims of forced sexual exploitation, 300,000 of them in Developed Economies and the EU. The ILO reported in 2016 that of the estimated 25 million persons in forced labor, 5 million were victims of sexual exploitation. However, due to the covertness of sex trafficking, obtaining accurate, reliable statistics poses a challenge for researchers. The global commercial profits for sexual slavery are estimated to be $99 billion, according to ILO. In 2005, the figure was given as $9 billion for the total human trafficking.

Sex trafficking typically occurs in situations from which escape is both difficult and dangerous. Networks of traffickers exist in every country. Therefore, victims are often trafficked across state and country lines which causes jurisdictional concerns and make cases difficult to prosecute.

In 2000, countries adopted a definition set forth by the United Moms. The United Nations Convention Against Transnational Organized Crime, Protocol to Prevent, Suppress and Punish Trafficking in Persons, Especially Women and Children, is also referred to as the Palermo Protocol. The Palermo Protocol created this definition. 147 of the 192 member states of the UN ratified the Palermo Protocol when it was published in 2000; as of September 2017, 171 states are parties. Article 3 of the Palermo Protocol states the definition as:

(a) "Trafficking in persons" shall mean the recruitment, transportation, transfer, harbouring or receipt of persons, by means of the threat or use of force or other forms of coercion, of abduction, of fraud, of deception, of the abuse of power or of a position of vulnerability or of the giving or receiving of payments or benefits to achieve the consent of a person having control over another person, for the purpose of exploitation.

Exploitation shall include, at a minimum, the exploitation of the prostitution of others or other forms of sexual exploitation, forced labour or services, slavery or practices similar to slavery, servitude or the removal of organs;

(b) The consent of a victim of trafficking in persons to the intended exploitation set forth in subparagraph (a) of this article shall be irrelevant where any of the means set forth in subparagraph (a) have been used;

(c) The recruitment, transportation, transfer, harbouring or receipt of a child for the purpose of exploitation shall be considered "trafficking in persons" even if this does not involve any of the means set forth in subparagraph (a) of this article;