National Grid plc is a British multinational electricity and gas utility company headquartered in London, United Kingdom. Its principal activities are in the United Kingdom (where it owns and operates electricity and gas transmission networks) and in the Northeastern United States (where as well as operating transmission networks, the company is a producer and supplier of electricity and gas). National Grid has a primary listing on the London Stock Exchange, and is a constituent of the FTSE 100 Index. It had a market capitalisation of approximately £31.4 billion as of 23 September 2021, the 26th-largest of any company with a primary listing on the London Stock Exchange.