Due to its transnational nature, at some level trafficking impacts virtually every country. Organizations that study migration patterns and trafficking classify countries as either "source," "transit" or "destination." In simple terms, the country of origin of a trafficking victim, the country where traffickers recruit women and girls, is known as a source country. Traffickers frequently move women through intermediary countries, often for extended periods when the women may be forced to work. These countries are known as transit countries. Traffickers choose transit countries based on their geographical location (near a border or a port), their weak border controls, corruption of immigration officials or their affiliation with the organized crime groups that are involved in trafficking. Transit countries generally have access to the destination country. Destination countries are those that receive trafficking victims. Destination countries are generally economically prosperous because they must be able to support the commercial sex industry.

A report by the British Home Office explains the relationship between source, transit and destination countries in this way: "Women are trafficked into countries that have existing sex industries which can absorb them, and are often trafficked from countries where there is an indigenous sex industry. They are possibly trafficked through one or more intervening 'transit' countries." From Stopping Traffic: Exploring the extent of, and responses to, trafficking in women for sexual exploitation in the UK, 2000, Liz Kelly and Linda Regan.

The classifications become complicated because many countries fit more than one category; they may serve as transit counties along a trafficking route and may also receive trafficking victims as a destination. The Protection Project, a legal human rights research institute based at the Johns Hopkins University School of Advanced International Studies in the U.S., has created a number of maps of trafficking routes that illustrate the trafficking patterns between source, transit and destination countries around the world.

It is vital that source, transit and destination countries cooperate and develop joint strategies to combat trafficking. According to the U.S. Department of State Trafficking in Persons Report for 2002, "Destination countries must work with transit and source countries to stem the flow of trafficking; source countries must work not only to prevent trafficking, but to help with the reintegration of trafficking victims back into their home societies."