Despite the profound challenge of integrating the new countries socially, economically and politically, this will create the largest free trade zone in the world.
However, as many of the new member states are significantly poorer than Western Europe, accessing funds for regional development may become increasingly difficult.
The 10 countries are Poland, Hungary, the Czech Republic, Slovakia, Slovenia, Estonia, Latvia, Lithuania, Cyprus and Malta, and they should be able to wrap up talks to join the EU by the end of the year, according to a recent report from the European Commission.
Twenty percent of the 38 million Polish population work in agriculture, and this is one area where competition between the regions will increase.
While the countries are poorer than existing members, they are all experiencing rapid economic growth.
Both Northern Ireland and the Irish Republic will suddenly have a much larger market for exports, analysts say.
But Eastern Europe will also offer international companies much cheaper labor.
The single economic and trade zone of the EU will have a combined population of 450 million.