National Grid is a holding company. Through its subsidiaries, Co. is an energy utility. Co.'s business units include: U.K. electricity transmission (ET), in which Co. owns and operates the high-voltage ET network in England and Wales; U.K. electricity distribution, in which Co. owns ad operates the electricity distribution networks for the Midlands, the South West and South Wales; U.K. electricity system operator (ESO), in which Co. operates as the ESO across Great Britain; and New England, in which Co. owns and operates electricity transmission facilities and distribution networks across Massachusetts, New Hampshire and Vermont as well as gas distribution networks across Massachusetts.