Since the foundation of the European Union in 1958, its extension has served as a political measure to create and save peace in Europe after the Second World War. Nearly 40 years later, the hopes for economic advantages of an accession have become more and more important. In view of the applications for accession of 10 countries of Central and Eastern Europe, one of the questions most interesting is the one discussed in this chapter: which conditions promote the reduction of initially existing developmental lags between the richer European Union member states and a less-developed accession country? Having identified those conditions one can look for possibilities of making the integration easier and faster in order to reduce the costs of integration and to exploit the benefits at an earlier point in time. Looking at the economic theory there are a lot of starting points to analyse economic catching-up processes. Here, one argument is taken based upon the new real theory of international trade as well as on regional economics, and which is tested in the following with data from the former southern enlargement of the European Union:
: A successful economic catching-up process goes along with an assimilation of industrial production structures of the accession candidate to those of the European Union as a whole.