The decarbonisation of the gas grids will be an integrated part of the future Smart Energy Systems. Gas is not just natural gas: it can also be renewable gas, produced from various feedstocks in the forms of biogas, biomethane, hydrogen or synthetic gas. Renewable gas can also be produced from excess electricity generated by variable renewable sources (such as solar and wind). The existing natural gas transport and distribution infrastructure is well developed and interconnected in Europe. Almost all member states have a natural gas distribution system, although in the Eastern EU countries gas infrastructure is mainly based on gas transit business and not domestic applications. Green hydrogen from renewable sources such as renewable electricity (via electrolysis) or from biomass (via gasification) is currently produced in small volumes that allow blending shares with methane and using existing gas infrastructure for pipeline transport. Currently existing dedicated hydrogen transport infrastructures are industrial clusters in Belgium, North of France and the Netherlands. Some projects have tested the viability of conversion of the pipeline and underground storage from natural gas to hydrogen. Current investments in large natural gas infrastructure are mainly driven by security of gas supply objectives, wholesale markets’ integration and shifts in gas supply. Some of these investments are questionable as it is expected that the existing gas infrastructure can cope with the future gas demands. However, the need and role for this infrastructure will likely change in the future, because of the need for increased security of supply or increased electrification in the heating sector. In most of the scenarios, the development of the gas networks and related storages will be strongly linked to power‐to‐gas technologies that can integrate more renewable energy and use the grids as chemical storage.