The UK launch of ‘The Fusion Doctrine’ in 2018 was a major event in the history of joined-up government. It diagnosed changes to the national security arena, principally the distributed nature of non-traditional threats and their responses, offering a way to promote best practice in strategy-making and implementation – all while placing a spotlight on cross-functional teams, accountability and annual review. Yet it is difficult to implement whole-of-government approaches outside of times of crisis to address longstanding subjects. Joe Fossey suggests that space may be an opportunity to develop Fusion practice, focus government departments to pool and direct resources, and organise Fusion doctrine for the long term.