Tackling defence corruption is about much more than stopping dodgy commissions on arms sales. Civilians and soldiers die because of corruption in defence, insecurity rises, peace is compromised, wars extended. This article describes the twenty-year effort by Transparency International’s Defence & Security Programme to reduce defence corruption across the whole sector, collaborating with and pressuring defence ministries, military forces, defence companies, NATO, NGOs and others. The defence sector is showing the way in several respects – comparative corruption-risk analyses, technical indexes, the professional communities of ethics officers in the defence companies, the roles of the Offices of Suspension and Debarment and the Inspectors General, the bravery of many government officials and ministers leading defence reform. The progress suggests that a ‘whole sector’ approach – covering companies, governments, regulators and civil society – can be effective, and may hold lessons for how reform approaches in other sectors can be better conceived and implemented.