Strategic Environmental Assessment (SEA) promotes sustainable development by mainstreaming environment into economic development at a national and local level. SEA is a well-established planning and environmental governance tool/system set out in the UNECE Protocol on SEA to the Convention on Environmental Impact Assessment (EIA) in a Transboundary Context. It ensures that development plans in key sectors such as energy, water and waste management or urban planning with likely significant adverse environmental impacts take into account environmental (and health) considerations. Since 2004 the UNECE secretariat has provided technical assistance and capacity building support to foster ratification of, and accession to, the Espoo Convention and its Protocol on SEA in the countries of Eastern Europe, Caucasus and Central Asia. The secretariat has a broad experience in assisting the countries in improving their legislative and institutional frameworks for the implementation of both treaties. The tailor made training and pilot projects provided by the UNECE have proven to be efficient in building the necessary institutional and human capacities in countries for the effective application of EIA and SEA to their development projects, plans and programmes.