In this thesis, Greek, Portuguese and Spanish accession of European Union is investigated. Agricultural production, consumption and trade patterns of Greece, Portugal and Spain have changed by the full application of Common Agricultural Policy. The commodity composition of these countries experienced an adjustment, too. The production of vegetables, fruits, fish and other typical Mediterranean products have increased. The composition of consumption has moved from low-income elastic products to high-income elastic products. The agricultural trade direction of these countries has shifted to the European Union. Trade with neighbouring EU member states increased relatively faster than the trade increase with other members of the European Union. Most of the trade volume of these countries is with the Mediterranean countries of the European Union.