The principle of proportionality is a key principle in EU law; however, it has distinctive meanings in different contexts. In the field of free movement, proportionality constrains the Member States’ possibilities to diverge from EU law on the basis of the requirement of suitability and necessity. In the area of EU competences it is a principle that guides the relationship between the EU and Member States and requires the EU legislator to use the least intrusive means of regulation/legislation to protect state sovereignty. There is also a third approach to proportionality in the field of EU sanctions and the Court of Justice’s case-law, which entails that the sanction imposed must be commensurate to the gravity of the offence. This more conventional criminal law ‘retrospective’ version of proportionality has now been enshrined in the Charter of Fundamental Rights and suggests that ‘the severity of penalties must not be disproportionate to the criminal offence’.