The traditional model of European Union (EU) enlargement is based on certain principles linked to the rights and duties of both applicant countries and current members. These principles have been applied successfully in previous enlargement rounds and may yet serve as a sound model for some applicant in the future. The scope of this paper is to consider some of the key economic dimension of EU enlargement, focusing on the characteristics of the new member states and on the economic implications of enlargement for the EU. Analysis showed that the overall economic effects of the 10 + 2 enlargement are positive. They are so particularly for the acceding countries, which have the prospect of clear gains, even if the costs are greater and many of the benefits are slower to arrive than they anticipated. For the EU-15, the direct economic gains are relatively modest, with enlargement not expected to bring much extra efficiency or growth, or to create many new jobs.