The present article aims to critically describe and compare how two rather different legal fora – the United States Supreme Court and the European Court of Human Rights – address the same constitutional issue: the protection of property rights and legitimate expectations in the face of a legal change. According to the US Federal Constitution, the effects of a legal change over patrimonial interests can be treated under the due process of law clause or the takings clause. Article 1 of Protocol No. 1 of the European Convention on Human Rights, alone or in conjunction with the right to a fair trial, plays the same role under the ECHR. Our concluding remarks will show that in both systems, property protection provisions amount to a guarantee against unfair governmental action. Regulatory takings and proportionality are areas of strong disagreement between the two systems, whereas retroactive legislation and patrimonial expectations reveal some interesting similarities.