While various forms of slavery and forced labor have existed throughout human history, trafficking in humans is a relatively new area of global concern, as specific laws date back only to 2000. As a legal concept, human trafficking is defined according to its requisite acts (recruitment, transport, harboring of victims), means (use of force, fraud, or coercion), and purpose (exploitation). As a basis for scholarly analysis and public policy, trafficking can be viewed in terms of multiple dimensions, as it constitutes a criminal activity, an egregious abuse of human rights, and a pervasive illicit market. Each of these frames suggests different scholarly approaches to examining trafficking, as well as different policy responses to combat it. For example, a criminal activity frame connotes a prosecutorial response toward traffickers by state agencies, while a human rights-based approach suggests increased attention and services to trafficking victims. There is a significant, though underdeveloped, body of scholarship on the causes of human trafficking. Broadly put, extant work focuses on economic, political, and demographic variables, each of which are part of the wider array of factors that can make trafficking more or less likely. Economic factors can be assessed at both micro and macro levels, ranging from the cost–benefit analyses of traffickers to macroeconomic factors such as poverty and globalization. Political correlates of trafficking include armed conflict, the presence of peacekeepers, and the strength and capacity of domestic political institutions. For their part, nongovernmental organizations (NGOs) can also play a significant role in shaping state responses to trafficking. As trafficking commonly involves the movement of people across borders, some of the same demographic factors that drive migration are also associated with trafficking flows. Taken as a whole, there are still many underexplored avenues for future research. While well over a thousand articles and books have been published on human trafficking since 2000, a majority of extant research is non-empirical in nature, including general overviews of trafficking or analyses of relevant laws. A key factor contributing to this relative dearth of empirical literature is the lack of comprehensive data that reflects the complex and nuanced nature of trafficking. Given the policy-relevant nature of human trafficking, as well as its implications for human rights, there remains a great need for additional evidence-based research in this area.