This paper presents basic data about Southeast Europe power systems and open discussion about infrastructure development, supporting electricity market establishment. The region of Southeast Europe has been passing through very intensive political and economical changes in last 15 years. Transition from state controlled economy to market conditions has been accelerated recently. One aspect of the transition is establishment of common electricity market, named South East Europe Energy Community. All power sectors in the region are going through turbulent processes of restructuring, market opening and privatization at the same time. Security of supply should be observed more carefully then ever on all three levels: national, regional and European.