In this paper I offer a normative account of development expertise. Although extending expertise beyond the traditional development experts to include local stakeholders, this normative account aims to delimit legitimate forms of expertise. I label this normative view third wave development expertise. Third wave expertise is distinguished from both the technocratic and the social constructivist views of development expertise. In particular, I discuss the notions of contributory and interactional expertise. Contributory expertise denotes the extent to which a group of agents possesses (tacit, embodied, or explicit) knowledge which can make a significant contribution to development decision-making, while interactional expertise denotes the extent to which they are able to communicate this knowledge meaningfully. While local stakeholders may possess contributory expertise in matters of their own development, they may lack interactional expertise to communicate this knowledge. Resolving this issue, I argue, requires a mediator who can interact with and between external experts and local stakeholders.