The biggest ever enlargement of the European Union both in terms of scope and diversity is scheduled to take place on the 1 of May 2004 when 10 of the 13 candidate countries are expected to join the Union. This constitutes a challenge both for the current member states and for candidate countries but at the same time opens significant new opportunities for businesses across Europe. A single set of trade rules, a single tariff, and a single set of administrative procedures in many areas will apply not only just across the existing member states but also across the single market of the enlarged Union. Many enterprises in candidate countries have understood the new opportunities linked to enlargement. Entrepreneurs are aware that new legislative requirements will have to be applied in areas such as standards and certification. However, it is often less clear to them what exactly is needed. In addition, most enterprises are unaware of the fact that the EU runs a large number of direct or indirect support measures in all candidate countries, which will help them to prepare their business for the enlarged single market. This paper is meant to raise the awareness of the impact which enlargement will have on business in the acceding countries and to provide useful links for further information on enlargement related issues. The paper concentrates on the following enterprise aspects of enlargement: the economic impact of enlargement, measures to improve business environment (including rules and EU standards for industrial products), EU support to small and medium-sized enterprises and the likely impact on some specific sectors (steel, automotive, pharmaceuticals, chemicals and textiles). It complements information of other services of the European Commission regarding e.g. the economic impact of enlargement, competition rules, company law, taxation issues, health and safety at work, education and training, and environmental protection.