Gradually establishing the free movement of goods, one of the four freedoms of the internal market, was one of the centre-pieces of early market integration in the EEC. This was pursued by internal and external measures. Article 9(1) of the original 1957 EEC Treaty (now Article 23(1) TEC) provided for the gradual establishment of a customs union between the Member States and a common customs tariff vis-à-vis third countries.

Internally, a customs union requires the elimination of customs duties and ‘charges having equivalent effect’ (Article 25 TEC) as well as of discriminatory or protectionist internal taxes (Article 90 TEC), plus the elimination of quantitative restrictions on imports and exports and ‘measures having equivalent effect’ (Articles 28 and 29 TEC).

Externally, the Common Customs Tariff is fixed by EC legislation in the form of Council regulations, which have been regularly updated since 1968. The Common Customs Tariff forms part of the Community's exclusive powers in the field of the Common Commercial Policy.

However, the establishment of a true internal market for goods freely circulating within the entire area of the EU was not only a ‘legislative’ task, pursued by rule-making through treaty norms as well as secondary legislation in the form of harmonisation directives and regulations. To a large extent, the common market is the ‘product’ of the ECJ.