The geopolitical and socio-economic changes in East-Central Europe that started at the beginning of the 1990s has brought about a fundamental change in the status of frontier areas in this region. The paper examines the new transborder relationships as well as the conditions, forms and dynamics of integration processes on the example of Poland. It discusses some stimuli and barriers to cross-border co-operation, including the creation of new transborder institutional embeddedness (e.g. Euroregions). On the other hand, the paper stresses the role of the informal economy in the current development of border zones in East-Central Europe.