"This paper aims to provide an overview of the information on human trafficking and prostitution gathered by the League of Nations during the 1920s and ‘30s. The organization's rich archives in Geneva contain a wealth of information on e.g., the working conditions of prostitutes active in more than a hundred cities worldwide, and prostitutes' backgrounds and motivations to enter into prostitution. They thus provide a unique instrument for the comparative study of human trafficking and commercial sex worldwide. The paper gives a short historical overview of the origins of anti-trafficking and the League's initial activism during the early 1920s; reviews the organization's enquiries on trafficking in women and children between the mid-1920s and early 1930s; and gives an account of the League's initiatives for the rehabilitation of prostitutes and prevention of prostitution."