This lesson examines the specific institutions and rules governing the gas market both at the EU level and at the national level. At EU level, the process of completing the gas market in the EU is being studied. At national level, and in the light of EU law, the role of the Energy Regulatory Authority and of the companies involved in the production, marketing, transport, distribution of natural gas is examined. The relationship between the companies involved in the vertical chain of activities which have as their object the production and exploitation of that energy source is also studied, on the one hand, as the relations between natural gas distribution and trading companies with the final consumer (industry and households) , Secondly. Cross-border, emphasis is placed on trans-national gas transmission networks.