WEC Energy Group Inc., based in Milwaukee, Wisconsin, provides electricity and natural gas to 4.4 million customers across four states through its brands – We Energies, Wisconsin Public Service, Peoples Gas, North Shore Gas, Michigan Gas Utilities and Minnesota Energy Resources.

WEC Energy Group's headquarters is located at 231 W. Michigan Street in Milwaukee.

On 29 July 2015, the company completed its acquisition of Integrys Energy Group in a deal worth $9.1 billion.

On May 3, 1995, Wisconsin Energy Corporation and Northern States Power Company (NYSE: NSP) each filed a Securities and Exchange Commission Form 8-K to combine in a merger-of-equals transaction to form Primergy Corporation. It would have been the 10th largest investor-owned electric and gas utility company in the United States, based on market capitalization at that time of about US$6.0 billion. NSP would have been the nominal survivor, and the merged company would be headquartered in Minneapolis (headquarters of the old NSP), but the merged company would have been registered in Wisconsin.

On May 16, 1997, both CEOs announced that the boards of directors of both companies had terminated the merger plan because of approval delays by the U.S. Department of Justice, the SEC, and state regulators in Minnesota and Wisconsin. They also stated that regulatory agencies were changing their merger policies as they were considering the companies' filing and that further delay would reduce the benefits of the Primergy transaction.

The delay already had put the merger five months behind schedule and had reduced earnings for both utilities by a total of US$58 million to that point. In addition, Wisconsin Energy's stock had fallen about 13% since early 1995 when the deal had been announced, while NSP's stock had risen by 6%. The case was considered to be a bellwether in the utilities industry, putting an end to the rapid pace of mergers and acquisitions that had been ongoing up to then.