As retailers in the North increasingly adopt codes of practice containing social and/or environmental provisions in global supply chains, there is a need for rigorous assessment of their social impact. Moving beyond the rhetoric, it is important to establish the actual impact of such codes on poorer workers, their families, and other local stakeholders. This paper sets out the key methodological and conceptual issues arising in such an assessment as identified by a three-year study on the South African wine industry. It reviews the different motivations and approaches employed by code bodies, donors, academics, and practitioners, and highlights the lack of workers' voices in the debate on corporate responsibility as well as some of the early research findings. Finally, it explains how the inherent power inequalities in global supply chains make it more difficult to adopt a truly empowering approach to assessing the impact of codes of practice.