This article is about proportionality, the political maxim. For other uses of the term proportionality, see Proportionality (disambiguation).

The principle of proportionality is a political maxim which states that any layer of government should not take any action that exceeds that which is necessary to achieve the objective of government. It was initially developed in the German legal system.

It is a fundamental principle of European Union law. According to this principle, the EU may only act to exactly the extent that is needed to achieve its objectives, and no further. This principle has underpinned the European Union since its inception in 1957. It is explicitly specified in the proposed new Treaty establishing a constitution for Europe.