Exelon Corporation (Exelon ) is a large U.S. utility company headquartered in Chicago. The company is listed on the stock index S & P 500 and the Dow Jones Utility Average. The company was formed in October 2000 by the merger of PECO Energy Company and Unicom from Philadelphia from Chicago (which Commonwealth Edison was one ). Exelon has 5.2 million customers in the energy supply of electricity and 460,000 customers in Philadelphia the power supply with gas. In June 2005, Exelon had interests in 19 nuclear power reactors in 11 nuclear power plants. The merger began on 30 June 2005 by Exelon with the company Public Service Electric and Gas Company of New Jersey failed.

In April 2011, Exelon bought the U.S. company Constellation Energy.

End of July 2013, EDF announced to pull on an option and Exelon its shares in the joint venture CENG to sell.