<p>This paper investigates how the Court of Justice of the European Union (CJEU) and the European Court of Human Rights (ECtHR) interpret autonomous concepts. Autonomous concepts are the product of a peculiar interpretative technique employed by the CJEU and ECtHR in order to harmonise legal language within a multilingual and multicultural legal space. To do so, these courts define and interpret a new terminology specifically for European Union law and the European Convention on Human Rights, declaring that they must be interpreted independently of any national or international meaning. The number of autonomous concepts, as well as the official languages, differ considerably between the two frames: the European Union counts 27 Member States and 24 official languages, while the Contracting Parties to the Convention are 46, with two official languages. Despite their differences, it appears that both courts employ this interpretative technique to solve the tension created by the various meanings that terms might have in domestic courts. To do so, they give new meaning to legal terms, thereby creating a detachment from the significance of national legal terms. This paper examines the case-law of both courts regarding the conceptual autonomy of legal terms and analyses their linguistic and argumentative patterns through the lens of corpus linguistic analysis. </p>