Subsidiarity is the principle that decisions should be made at the lowest, smallest, closest level that can handle them — and only pushed up to a bigger body when the smaller one genuinely cannot do the job. The village decides village things; the country decides country things; only what neither can manage alone goes higher. You will meet this word almost entirely in one place: European Union politics. It is written into EU treaties, and it is the answer Brussels gives to the complaint 'you are deciding too much for us' — the EU is supposed to act only when member countries cannot achieve something well enough by themselves. Because of that history the word has a political taste: people who use it are often arguing about how much power the centre should have. The idea itself is older than the EU and came out of Catholic social teaching, where the argument was that a larger body should not swallow the work a smaller community can do for itself. That older use still turns up in writing about the church, and sometimes in discussions of local government or company structure generally. This is a specialist word — political science, EU documents, serious newspapers. No one uses it over dinner, and A1-A2 students meet it only in reading, not in speaking.

輔助原則（歐盟用語：能由地方或會員國自己決定的事，就不要交給上層／布魯塞爾決定）。中文有時也譯「補充性原則」。