This article investigates perceptions of the extent to which non-governmental organization (NGO) peer regulation initiatives have been effective in enhancing accountability in the humanitarian sector. It is based upon semi-structured interviews with individuals with responsibility for accountability policy from leading NGOs and focuses on two of the best-known initiatives: Humanitarian Accountability Partnership and Sphere. It finds that the initiatives have prompted positive changes in practice, but there are significant concerns about their deleterious impacts. Participants describe a host of challenges, including the tendency of peer regulation to become excessively bureaucratic and labour intensive. They cast some doubt on the potential of the initiatives to assist NGOs to be more accountable to affected communities. Copyright © 2014 John Wiley & Sons, Ltd.