Kmart (sometimes styled as "K-Mart") is a chain of discount department stores in the United States, Puerto Rico, the U.S. Virgin Islands, and Guam. The chain acquired Sears in 2005, forming a new corporation under the name Sears Holdings Corporation. Kmart also exists in Australia and New Zealand (see Kmart Australia), although it now has no relation to the American stores except in name, after U.S. equity in the Australian business was purchased in the late 1970s. Kmart is the third largest discount store chain in the world, behind Wal-Mart and Target; all three chains were founded in 1962.

As of January 28, 2006, Kmart operated a total of 1,416 Kmart stores across 49 states, Guam, Puerto Rico, and the U.S. Virgin Islands. This store count included 1,361 discount stores, averaging 92,000 sq ft (8,500 m2), and 55 Super Centers, averaging 165,000 sq ft (15,300 m2).

Kmart's world headquarters were located in Troy, Michigan, in a sprawling complex which, since Kmart's relocation to Illinois, has been slated for demolition. However, at this current time, no actual demolition efforts are underway, and the proposed mixed-use complex the Pavilions of Troy, slated for the site has not begun construction due to issues with funding.

Kmart became known for its "Blue Light Specials." They occurred at surprise moments when a store worker would light up a mobile police light and offer a discount in a specific department of the store. At the height of Kmart's popularity, the phrase "attention Kmart shoppers" also entered into the American pop psyche, appearing in films and other media such as Rain Man, Troop Beverly Hills, Six Days Seven Nights, and Beetlejuice.