Abstract
The meaning of the general principles of EU law has been broadly developed by the Court of Justice of the European Union; however, for many years it had only limited competence in deciding criminal cases. The principle of direct effect is important for ensuring the efficient functioning of EU law. The aim of this research is to find out if and how this principle affects criminal justice. To reach this objective, the researchers examine how the substance and content of the principle, through the doctrine and the judgments of Court of Justice of the European Union, can influence national criminal law and criminal procedure. Afterwards, the actual impact of EU law on national criminal law is evaluated, taking Lithuania as an example. The analysis reveals that direct application of directives in material criminal law is highly unlikely, while in criminal procedural, law such a possibility is real if EU norms are clear, unconditional, and precise.