Cinergy Corp. NYSE: CIN was an energy company based in Cincinnati, Ohio. Cinergy was created on October 24, 1994, from the merger of the Cincinnati Gas & Electric Company (CG&E) with PSI Energy and later included Union Light, Heat & Power (ULH&P) as well.

In 1996, Riverfront Stadium in Downtown Cincinnati was renamed "Cinergy Field" in a sponsorship deal with Cinergy. The stadium was demolished by implosion in December 2002 to make way for Great American Ballpark.

In 2005, Cinergy announced a friendly acquisition by the larger Charlotte, North Carolina-based Duke Energy. The acquisition was completed on April 3, 2006. The combined company retains the Duke Energy name. Until the acquisition, Cinergy still operated under the names of the three local utilities (e.g., Cinergy/CG&E in Cincinnati); since the acquisition, the names of the three utilities and Duke Power have been phased out.

In May 2006, Cinergy was fingered as a key contributor to major pollution in the American Midwest, prompting the New York State government to sue the company and forcing the company to install modern pollution control equipment. The Ontario government, across the border in Canada, has followed suit at the request of New York Attorney General Eliot Spitzer.