Introduction: In 1977 the European Council adopted the ‘Directive Concerning Mutual Assistance by the competent Authorities of the Member States in the Field of Direct Taxation’.3 The implementation deadline of this Directive was 1 January 1979. On 6 December 1979 the Council adopted an amendment to the Directive, extending its scope to value added tax (VAT), an extension which was rescinded by an amendment of 2003.4 However, it was not until 1992 that the Court of Justice of the European Communities (ECJ) made its first reference to the Directive. This was on 28 January 1992 in the Bachman case and the Commission v. Belgium case.5 Between 1 January 1992 and 1 May 2009 the ECJ referred to the Directive in 35 cases (34 judgments and one order). In this paper I analyse these cases with regard to the different types of references to the Directive that can be distinguished and the way references to the Directive have evolved over time. A summary of the most important features of all cases which have regard to the Directive is included in Annex I to this paper. As the references in several cases were derived from the purpose of the Directive, I start with the purpose of the Directive as defined by the ECJ.