With the coming into force of the Treaty of Lisbon, the competences of the European Union in the realm of criminal law have greatly expanded. The EU, in a multitude of legislative instruments, requires its Member States to criminalize a big variety of harmful conducts. However, the criminal law legislation of the EU has, so far, almost exclusively focused on specific criminal offenses and has failed to develop and define general principles of criminal law. The EU frequently refers to conduct, attempt, and participation in its legislation, but fails to determine what these concepts should...