Integrated European Gas Market is understood as enhanced cooperation and functioning of the system as a whole, including: interconnections between systems, liberalization of the single European Market achieved by harmonized access conditions to the transmission networks and the application of the principles of non-discrimination, transparency and objectivity for the organization of the Gas Market as a whole. The process has shown that this cannot be achieved without close cooperation between TSOs and other operators, NRAs, MSs, European Commission. To achieve harmonization and cooperation and the application of the 3 principles, the legislative framework had to be amended/ extended multiple times: Directive 2003/55/EC; Regulation (EC) 1775/2005; Directive 2009/73/EC; Regulation (EC) 715/2009 (amended in November 2010); Regulation (EC) 713/2009. The European integrated market will be a reality providing that common practices can be found and applied all across Europe, in particular on the following four issues below: capacity model (used to define the available interconnection capacities between two countries taking into account the daily parameters), Capacity Allocation Mechanism (CAM), Balancing, Tariffs, Data exchange, Governance (strong and flexible governance structure to be designed to gather all regional initiatives under a Pan European Governance).