ENTSO-E, the European Network of Transmission System Operators, represents 43 electricity transmission system operators (TSOs)​ from 36 countries across Europe. ENTSO-E was established and given legal mandates​ by the EU’s Third Legislative Package for the Internal Energy Market in 2009, which aims at further liberalising the gas and electricity markets in the EU.

The role of Transmission System Operators has considerably evolved with the Third Energy Package. Due to unbundling and the liberalisation of the energy market TSOs have become the meeting place for the various players to interact on the market place.