Nudges with paternalistic aims pose special legal problems in liberal States. Surprisingly, the discussion on regulation-by-nudging has not focused on the constitutional limits to nudging. But judges may at one point be confronted with a nudge regulation challenged by the individuals being nudged; and even before reaching a court, the legality of nudging should be scrutinized by legislators. In this chapter, the legal limits of nudging under the European Convention of Human Rights and the Charter of Fundamental Rights are explored with a special view on the different (legitimate) aims of nudging, that is, paternalistic and non-paternalistic nudges (targeting externalities and public goods/bads). Different types of nudges are scrutinized by applying the proportionality principle. Whereas some nudges pass the test easily, others might fail the test. The analysis can be extended mutatis mutandis to other human rights protection instruments and constitutions.