Midwest Airlines (formerly Midwest Express) was a U.S.-based airline and, for a short time, an operating brand of Republic Airways Holdings based in Oak Creek, Wisconsin, operating from Milwaukee's General Mitchell International Airport. On April 13, 2010, parent company Republic announced that Midwest Airlines and Frontier Airlines would merge, with the Midwest brand disappearing in late 2011.

Midwest Airlines' final flight operated with a Boeing 717-200 and staffed with Midwest Airlines flight crews landed in Milwaukee on November 2, 2009. Effective November 3, 2009, Midwest Airlines ceased to exist as an actual operating airline (allowing its DOT air carrier operator certificate to lapse).

Midwest Airlines began its existence in 1948, when Kimberly-Clark began providing air transportation for company executives and engineers between the company's Neenah, Wisconsin headquarters and its mills. Operating out of the nearby Appleton airport, early employee shuttle destinations included Chicago O'Hare, Memphis, and Atlanta's Fulton County Airport.

In 1969, K-C Aviation was born from this, and was dedicated to the maintenance of corporate aircraft. Kimberly-Clark moved its corporate headquarters in 1985 to Irving, Texas, a suburb of Dallas. K-C Aviation was sold in 1998 to Gulfstream Aerospace for $250 million; included were its operations in Appleton, Dallas, and Westfield, Massachusetts.

After the Airline Deregulation Act of 1978, Kimberly-Clark and K-C Aviation decided to form a regular scheduled passenger airline, and out of that initiative, Midwest Express began operations on June 11, 1984. At the time the airline had two Douglas DC-9-10s and 83 employees. Early plans for the airline called for it to serve Appleton, Chicago, and Atlanta. Kimberly-Clark opted against this plan after local resistance over the carrier's desire to serve Atlanta's Fulton County Airport, which is a general aviation airport on the city's west side. From 1983 to 1985, the airline also operated a single Convair 580 twin turboprop aircraft from Kimberly-Clark's corporate aviation department.

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