When a new runway apron, fuel depot or passenger terminal opens on a European air base, people usually call it a NATO project, and they are rarely wrong. They are, however, rarely complete. The money that NATO’s allies pool for military infrastructure pays for works that the Alliance has approved as a collective requirement, within a scope and a spending ceiling set project by project. Around that authorised core sit costs that the common fund was never meant to carry: equipment the host country buys for itself, works judged ineligible for common funding, taxes, the design and supervision of national contributions, recurring utilities and maintenance, and, where allied forces are stationed under bilateral arrangements, support that the host state has agreed to supply at its own expense. European governments are raising defence budgets and the Alliance is enlarging its common-funded programmes. The practical question is therefore no longer simply how much NATO spends on infrastructure. It is where common-funding eligibility ends on a given site, which authority turns an approved requirement into a contract, and which public budget remains responsible for the inputs that make an asset usable and keep it in use.