Europe is now a single power market on which energy is traded from Poland to Portugal. The UCTE’s ‘Security Cell Principle’ guarantees that pan-European electricity trading can rely on an invisible, albeit highly efficient technological basis. Harmonized rules for this basis have been developed by the UCTE members themselves and set forth in the ‘Operational Handbook.’ The ‘Multilateral Agreement’ is a set of contracts according to which the member states have committed themselves to comply with and monitor these rules.