Krystal is an American regional fast food restaurant chain headquartered in Dunwoody, Georgia, with restaurants primarily in the Southeastern United States. It is known for its small, square hamburgers, called sliders in places other than the Southeast, with steamed-in onions. Krystal moved its headquarters from Chattanooga, Tennessee, where it had been based since 1932, to the Atlanta suburb of Dunwoody in early 2013.

Founded on October 24, 1932, in Chattanooga, Tennessee, during the first years of the Great Depression, entrepreneur Rody Davenport Jr. and partner J. Glenn Sherrill theorized that even in a severe economic upheaval, "People would patronize a restaurant that was kept spotlessly clean, where they could get a good meal with courteous service at the lowest possible price." The restaurant's first customer, French Jenkins, ordered six "Krystals" and a cup of coffee, all for the price of 35¢ ($8.20 in 2025's dollars), thus proving their theory true according to the company's own keeping of history.

Davenport had visited Chicago's White Castle restaurants, taking notes of successful features, before setting forth on his own venture. Davenport and Sherrill set up the first Krystal at the corner of 7th and Cherry Streets in Chattanooga. The first Krystal was a modular building constructed in Chicago and shipped to Chattanooga for final installation. The oldest Krystal still in operation is located on Cherokee Boulevard in Chattanooga's Northshore District. Krystal is the seventh or eighth-oldest hamburger chain in the United States (the oldest being White Castle) and the oldest in the South.

Regarding the origins of the Krystal name, company legend states that Davenport and his wife were riding down a mountain road when Mrs. Mary McGee Davenport saw a lawn ornament in the shape of a crystal ball. While gazing at the lawn ornament, Mrs. Davenport commented that since Davenport and Sherrill felt cleanliness was a cornerstone of the concept, they should name the restaurant Crystal for "clean as a crystal"—yet with a "K" to add a little twist. Krystal's restaurants through the years often sported a crystal ball on the top.

From the early 1930s through the early 1960s, the chain served much of its food not in take-out containers but on inexpensive porcelain dishes with the "Krystal" moniker. The waiters and waitresses wore white uniforms, and food was offered through counter service. In the 1950s, Krystal opened its first drive-through window, which most locations maintain today. A 2013 study of seven fast food franchises found that service at Krystal drive-throughs was the slowest, with an average wait time of 218 seconds. It was, however, the most accurate in terms of fulfilling orders.

In the 1950s, cake doughnuts were served as a breakfast and dessert item. From about 1970 until 1986, "bone-in" kettle fried chicken and related sides were offered. These items were sometimes sold from a stand-alone addition to the hamburger restaurants.

DavCo, a division of Krystal, operated Wendy's franchises from the 1960s until 2017, when the franchises were bought back by Wendy's and sold to NPC International. Between 1983 and 1988, DavCo also operated the Po' Folks family restaurant chain.

Krystal restaurants, both company-owned and franchised, operate in Alabama, Florida, Georgia, Kentucky, Louisiana, Mississippi, New Jersey, South Carolina, North Carolina, New Jersey, Tennessee, and Arkansas. Krystal has also operated several restaurants in Texas over the years. It is often compared to the northern restaurant chain White Castle, and other than the South Central Kentucky and Nashville, Tennessee markets, the two restaurants' market areas do not generally overlap.