AbstractThe proportionality principle plays a key role in constitutional review of public acts. Its use legitimises the constitutional claims of EU law in the context of a multi-level polity system. The application of proportionality in the EU differs based on whether legal acts of the EU or of its Member States are concerned. In the former case, a manifestly disproportionate test is usually applied, while in the latter case, a least restrictive means test (LRM) is normally used. Both are conditioned by the degree of integration achieved. In future, the use of the principle may involve increasing attention being paid to individual rights.