In this paper the concept of tax co-ordination within the European Union (EU) is discussed, in view of the coming enlargement of the EU. The tax externalities that possibly arise in a single market are analysed, as well as the ways these externalities can be prevented or internalised. These theoretical reflections are placed alongside the actual system of tax co-ordination within the EU. Focusing on VAT and corporate taxation, the implications of enlargement of the EU for the tax co-ordination issue are discussed
