This thesis introduces and defends a vulnerability theory of exploitation and uses that theory to explain what is exploitative about international transactions such as commercial gestational surrogacy and clinical trials. The vulnerability theory is preferable to a number of alternative theories of exploitation that have been defended in the philosophical literature. The dominant theories of exploitation tend to be inadequate or incomplete to account for different forms of exploitation. These shortcomings stem from the theories’ tendency to mistake something that is characteristic of specific forms of exploitation for what constitutes exploitation itself. Meanwhile, according to the vulnerability theory, exploitation occurs when A derives benefit by taking advantage of the vulnerability and dependence of B. This conceptualisation of exploitation as a function of the levels of vulnerability and dependence between transactors is analytically advantageous because it identifies conditions for exploitation that characterise most forms of exploitation. This conception also renders exploitation in the international domain visible by highlighting the prevalence of vulnerability and dependence therefore demanding theorisation, which until recently has been absent. Lastly, the project argues that exploitation at the international domain is distinctively wrong for reasons that do not arise in transactions between compatriots and challenges the idea of global justice.