Transposition is the process of incorporating EU directives into the national laws of EU Member States.

Unlike regulations and decisions, directives are not directly applicable throughout Member States but require national laws to incorporate their rules into national legislation. The Member States must adopt these national measures by a deadline, which is specified in the directive. Member States must notify their national implementing measures to the European Commission.

• The communication which the Member States must make in accordance with the principle of sincere cooperation referred to in Article 4(3) TEU must contain sufficiently clear and precise information as to the content of the national provisions transposing the directive. That communication, which may be accompanied by a correlation table, must therefore clearly indicate those laws, regulations and administrative provisions which the Member State considers to have complied with the various obligations imposed on it by the directive. Failure by a Member State to comply with that obligation, whether due to a total or partial absence of information or to insufficiently clear and precise information, may in itself justify the initiation of proceedings under Article 258 TFEU (Judgment of 8 July 2019, Commission v Belgium (Article 260(3) TFEU — High-speed networks) (C-543/17, EU:C:2019:573, paragraph 51).
• The Court held, in particular, that although the transposition of a directive may be ensured by national legislation already in force, a Member State is not relieved of the formal obligation to notify it to the Commission even if it has already notified it in the context of the transposition of previous directives. (Judgment of 16 July 2009, Commission v Ireland (C-427/07, EU:C:2009:457, paragraphs 108 and 109).
• Where a directive provides that the measures transposing it must contain a reference to the directive or be accompanied by such a reference on the occasion of their official publication, it is necessary to adopt specific transposition measures (Judgment of 15 April 2010, Commission v Ireland (C-294/09, not published, EU:C:2010:200, paragraph 17).
• It is also settled case-law that, in proceedings under Article 258 TFEU, whether a Member State has failed to fulfil its obligations is determined by reference to the situation prevailing in the Member State at the end of the period laid down in the reasoned opinion, and the Court cannot take into account subsequent changes (Judgment of 28 March 2019, Commission v Ireland (Waste water collection and treatment system) (C-427/17, not published, EU:C:2019:269, paragraph 42).