Annotation: The principles of criminal proceedings are generally recognized standards that define the essence of criminal proceedings, ensuring the protection of the rights, freedoms and legitimate interests of participants in criminal proceedings. One of such principles is the principle of legality. This article describes the principle of legality and considers trends in its implementation in the activities of the European Court of Human Rights. Particular attention is paid to studying the content of the concept of “legality”, as it is interpreted by the European Court of Human Rights, the principles of criminal justice of the European Union are defined. The problem of legality is one of the centralities in the general theory of state and law. Its relevance is obvious both from a theoretical and practical point of view. The importance of this problem is explained by the fact that the concept of legality is inextricably linked with such institutions and parties of the state-legal life of society as the functions of the state, law-making, forms of realization of law, democracy, law, freedom and responsibility of the individual.