Polish membership in the European Union and the conversion of Polish-Ukrainian and Polish-Belarusian border into EU's external border, has undoubtedly influenced the relations and co-operation in the trans-border region. Therefore, it was important to analyse both the scale and the scope of these changes, as well as the new role of different actors in trans-border co-operation. Hence, in this book, special attention is given to finding the answer to the question of whether the enlarged EU will emerge as a "Fortress Europe" or as a "Golden Curtain". Considering this, the challenges for the study was to present the role of the trans-border co-operation for regional and local development, the factors affecting cross-border co-operation, the perception of co-operation in the eyes of regional and local stakeholders, the evaluation of established EU-financed programmes and the role of the institutions and the role of the institutions in promoting cross-border co-operation.