Natural gas provides significant energy supply, but also important flexibility services, especially in markets where winter heating load is high, and gas also provides flexibility and system services in power generation. These services are likely to become increasingly important as energy systems transition to lower carbon. But natural gas production and combustion must be phased out in a low carbon economy in applications where carbon capture and storage is not deployed. Options exist for decarbonizing the gas grid, enabling flexibility to be delivered with existing infrastructure. These include biologically derived methane, synthetic methane, and low carbon hydrogen, all potentially in a global context and deployed in sectors where decarbonisation is more difficult. Electric and hydrogen powered vehicles offer crucial routes to addressing transport emissions. These also have significant potential to be flexible users of electricity, facilitating the integration of renewable generation. Future planning and policy options need to consider these options in an integrated, long-term approach.