In 1957, the six aforementioned countries signed the Treaties of Rome, creating the European Atomic Energy Community (EURATOM) and the European Economic Community (EEC). This, in turn, resulted in the Member States pledging to remove trade barriers and to form a Common Market. In 1967, the institutions of the ECSC, the EURATOM and the EEC were merged, forming the European Commission, the Council of Ministers and the European Parliament.

Economic and political integration between the Member States of the EU has led to these countries taking joint decisions in several fields. A common policy has been developed in trade with third countries, as well as in consumer affairs, competition, environment, agriculture, energy and transport.

The Single Market was formally completed at the end of 1992; it has taken the Member States several years to transform the Common Market into a genuine Single Market where the intention is that Goods, Services, Persons and Capital are able to move freely (the "Four Freedoms"). During the 1990s, passport and customs controls were abolished at most of the EU's internal borders. Despite formal completion, the Commission proposes legislation several times each year for continued harmonisation of laws in both goods and services, aiming constantly to achieve a smoothly functioning Internal Market and remove all intra-Community barriers to trade.

The European Union, was created only in November 1993, i.e., when the Treaty of Maastricht on European Union came into force. Since then, the much longer established European Community, or EC, comprises only one of the three pillars that constitute the European Union.

In short, while the first full customs union was originally known as the European Economic Community, established by the Treaty of Rome in 1957, this later changed to the European Community which is now the first pillar of the European Union. The second pillar is on the Common Foreign and Security Policy (CFSP) and the third pillar is on Justice and Home Affairs (JHA). It is the law of the European Community pillar which occupies this Business Guide, as it is the most relevant pillar for international and intra-Community commerce.

In this sense, the law applied to traders - whether laid out in technical regulations, the customs code, trade defence measures, or monetary systems (among others) - are all, strictly speaking, matters of EC law. That said, it has become equally common to use the overarching term, namely, EU law, in common business parlance, due to the fact that EC law is such an important pillar of EU law. The term EU is likewise used when referring to the union of Member States.