Although it is not present in the EU Treaties, the principle of legal certainty has assumed over time, and still constitutes, a fundamental general principle in the context of EU law. The principle has been introduced into the EU legal order by the Court of Justice, by way of case law; the CJEU borrowed it from the legal traditions of the Member States, but then gave it its own scope and dimension, making it a cardinal principle of its own system. The following work traces the stages of its development, focusing on specific applications of the principle within certain areas of EU law.