<p>This article examines the politics of anti-corruption, with a particular focus on 'building integrity', which has emerged as a new concept in the field. Since the early 2010s, NATO and its member states in particular have invested in integrity mechanisms and practices to reduce the risk of corruption and to embed integrity principles in the defence establishments of NATO itself, its member states and partner countries. Using the concept of 'building integrity', this article seeks to show how this policy has been pursued while facing the reality of the persistence of corruption. While influential studies point to the existence of corruption, this article seeks to further the understanding of the fight against corruption by assessing the emergence and rise of the concept of 'building integrity' as a norm of defence and anti-corruption policy. Applying a social constructivist perspective, the article examines whether and how 'building integrity' has acted as a channel for the diffusion of anti-corruption ideas. The article suggests that engagement with the concept of 'building integrity' has provided an opportunity for the diffusion of an anti-corruption norm within the defence establishment.</p>