Regional spatial planning policies and tools for spatial development play an important role when applying sustainable development principles as they are outlined in the European Spatial Development Perspective (ESDP), by the European Spatial Planning Observation Network (ESPON) or by the European Conference of Ministers Responsible for Regional Planning (CEMAT). These principles combine economic, environmental and social objectives. It is necessary to verify how the principles may be applied to spatial planning and how to assess current planning tools, especially in polycentric development, with regard to sustainability. POLY.DEV deals with the demand for increasing knowledge and for developing a common strategy towards principles of sustainable polycentric development in order to avoid extreme polarisation around few centres and marginalisation of peripheral areas. Moreover, natural and cultural heritage should be managed in a balanced way through participative decision-making processes. The regions involved in POLY.DEV want to promote sustainable spatial polycentric development as a tool for balancing development with environment and cultural heritage preservation. The project partners of POLY.DEV come from Central and South-Eastern Europe. Partnership members are regional, provincial and local administrative bodies, development agencies and universities. The partnership equally involves scientific and administrative bodies, consultants and operative units. Expected Results: The POLY.DEV project is intended to make regional and local communities aware of gaps in spatial planning concerning principles outlined by ESDP, ESPON and CEMAT and to increase the skills and capacities of regional and local institutions in charge of land planning and governance to develop sustainable strategies. Moreover, it will assess different ways of influencing social and economic issues by spatial planning. POLY.DEV experiments and validates the application of forecasting patterns and strategies for sustainable polycentric spatial planning.