The relevance of the study is that the concept of due process, although it is one of the most general and at the same time fundamental phenomena of any democratic state of law of the present, however, for the legal system of Ukraine, it is quite recent and under-researched. The aim of the study is to ascertain the essence and content of the application of due process as a task of criminal proceedings. The methodological basis of the research was general scientific and special methods, namely dialectical, hermeneutic, teleological, logical, historical, statistical, formal legal and comparative legal methods. The author examined the genesis of the concept of "due process", in particular in the legal system of England and the United States of America, as well as at the level of current international treaties. The concept of "due process" was analysed, the author's definition was derived, according to which this is an order of implementation of legally significant actions, which embodies in practice the rule of law by applying to each person those norms of law that completely correspond to all important objectively existing circumstances and allow and predict in advance such application and its results. A brief overview of the regulatory provisions that make up the content of due process was provided. It was determined that the essence of due process is related to ensuring the sustainability of the social contract. Due process of law is the basic guarantee of preventing the arbitrariness of power, unlawful coercion and pressure on the population of the state. The difference between the "application of due process" and "ensuring the correct application of the law" as a task of criminal proceedings in different historical periods was analysed. It was proposed to attribute the application of due process to assurance tasks, which is aimed at limiting the general task -to ensure prompt, complete and impartial investigation and trial. The importance of applying due process in criminal proceedings, in particular, when there were gaps or conflicts of law, was characterised. It was determined that the Verkhovna Rada of Ukraine, the Constitutional Court of Ukraine, the European Court of Human Rights, and the Supreme Court are institutions are the bodies, which formalise the content of due process. The results of the study can be used both in practical activities to ensure the effective implementation of due process of law and in scientific and educational activities.