Hydro One Incorporated delivers electricity across the Canadian province of Ontario. It is a Crown corporation wholly owned by the provincial government.

Hydro One traces its history to the early 20th century to the establishment of the Hydro-Electric Power Commission of Ontario, renamed as "Ontario Hydro" in 1974.

In October, 1998 the provincial government passed the "Energy Competition Act" which restructured Ontario Hydro with the aim of privatizing all electrical generating and transmission/delivery.

Ontario Hydro was restructured on April 1, 1999 into three separate entities: Ontario Power Generation, the Ontario Hydro Services Company, and the Independent Electricity Market Operator.

On May 1, 2000 the Ontario Hydro Services Company was renamed Hydro One Incorporated and reorganized as a holding company with five subsidiaries:

• Hydro One Networks Inc.
• Hydro One Remote Communities Inc.
• Hydro One Markets Inc.
• Hydro One Telecom Inc.
• Ontario Hydro Energy Inc.

Between 1998 to 2000, Hydro One acquired 88 municipal electrical utilities. Numerous local/municipal distribution companies were also consolidated during this time.

In December 2001 the provincial government announced the intention to sell Hydro One under an initial public offering, however by April 2002 various groups in opposition to the plan were able to successfully challenge the government in the Supreme Court of Ontario , forcing a halt to the IPO.

In May 2002 the provincial government went ahead with the launch of an open electricity market, even though generating and distribution were remaining under control of the government.