Spirit Airlines, Inc. (NASDAQ: SAVE) is an American ultra-low-cost carrier headquartered in Miramar, Florida. Spirit operates scheduled flights throughout the United States and in the Caribbean, Mexico, Latin America, and South America. The airline operates bases at Atlantic City, Chicago–O'Hare, Dallas/Fort Worth, Detroit, Fort Lauderdale and Las Vegas. As of 2017, Spirit remains the only 2-star airline in the United States, reflecting the lowest service standards per Skytrax Airline Quality Research.

The company initially started as Clipper Trucking Company in 1964. The company changed its name to Ground Air Transfer, Inc., in 1974. The airline service was founded in 1980 in Macomb County, Michigan, by Ned Homfeld as Charter One, a Detroit-based charter tour operator providing travel packages to entertainment destinations such as Atlantic City, Las Vegas, and the Bahamas. In 1990, Charter One began scheduled service from Boston and Providence, Rhode Island, to Atlantic City. On May 29, 1992, Charter One brought jet aircraft into the fleet and changed its name to Spirit Airlines. Scheduled flights between Detroit and Atlantic City began on June 1, 1992. Scheduled flights between Boston and Providence began on June 15, 1992.

On April 2, 1993, Spirit Airlines began scheduled service to Orlando, Fort Lauderdale, and St. Petersburg, Florida. Flights between Atlantic City and Fort Myers, Florida, began on September 25, 1993. Service at Philadelphia began in 1994. During the next five years, Spirit expanded further, increasing service from Detroit and adding service in new markets such as Myrtle Beach, Los Angeles, and New York City.

In Summer 1994, Spirit Airlines overbooked flights, and 1,400 customers' tickets were canceled. The overbooking occurred because Spirit Airlines had given incorrect instructions to travel agents, causing those tickets not to be valid, even though the customers had paid for the flights. In response to criticism, Spirit Airlines said it would make sure all paid customers would always be able to fly to their destination, even if Spirit Airlines had to book them on a competitor's airline.

Spirit initially had their headquarters in Eastpointe, Michigan (formerly East Detroit) in Metro Detroit. It relocated its headquarters in November 1999, moving to Miramar, Florida in the Miami Metropolitan Area. Prior to the decision to move the headquarters to Miramar, Spirit considered Atlantic City, New Jersey and Detroit, Michigan.

In 2000, the US Federal Aviation Administration (FAA) proposed to fine Spirit Airlines $67,000 for allegedly violating federal regulations on cabin and seat markings and placards. Discrepancies were found in the marking and placarding of emergency equipment, passenger seats, storage areas and doors on eight of Spirit's DC9 and MD80 aircraft.

In November 2001, Spirit inaugurated service to San Juan, Puerto Rico, and implemented a fully integrated Spanish-language customer service plan including a website and dedicated reservation line.

In the fall of 2003, Spirit resumed flights to Washington, D.C.'s Ronald Reagan Washington National Airport, which were suspended after the September 11 attacks. Spirit also began service to Grand Cayman, San Francisco, and Boston in 2006, and in 2007 filed DOT applications to offer service to Costa Rica, Haiti, the Netherlands Antilles and Venezuela.

In 2006, Spirit exercised options to order 30 Airbus A320-200 aircraft for further expansion. Deliveries began in March 2010.

On March 6, 2007, Spirit began a transition to an ultra low-cost carrier. Their initial plan was to begin charging US$10 per checked bag for the first two bags, $5 if bags are reserved before 24 hours prior to the flight, in addition to charging $1 for drinks which were previously complimentary.

On June 3, 2008, Spirit Airlines made a WARN (Worker Adjustment and Retraining Notice) application to potentially relocate or lay off hundreds of pilots and flight attendants, and the closure of their San Juan and LaGuardia crew bases. In September 2008, Spirit began advertising on the side of aircraft, overhead bins, tray tables, seatback inserts and bulkheads.

In May 2009, Spirit pilots overwhelmingly voted in favor of strike action (98% of votes) due to stalled contract negotiations with management. Areas of dispute included compensation, work rules and benefits. At that time, Spirit pilots were among the lowest paid Airbus pilots in the United States.

On June 20, 2010, Spirit Plus was rebranded as "Big Front Seat" and business class service was discontinued. For an additional fee, a person could choose "Big Front Seat", or upgrade at the airport. In December 2010, Spirit Airlines introduced the Free Spirit World MasterCard.

On June 12, 2010, Spirit grounded its flights when its unionized pilots walked out on strike, stranding thousands of passengers. The ultimately successful pilot strike came after more than four years of inconclusive negotiations between the airline and the Air Line Pilots Association (ALPA), which represents Spirit's pilots. On June 15, negotiations between the airline and ALPA resumed, and a tentative agreement was reached late in the evening on June 16. The tentative agreement, which Spirit pilots later ratified by a 74% margin, brought the Spirit pilots' compensation and benefits in line with comparable U.S. Airbus operators. Flights eventually resumed. Of particular note, is that this was the first legal industrial action (strike) by U.S. ALPA represented pilots since 2005 (Polar Air Cargo), and the first passenger airline strike by U.S. ALPA represented pilots since 2001 (Comair).

In April 2012, citing the airline's strict refund policy, Spirit Airlines representative Misty Pinson announced that the airline would not issue a refund to dying veteran Jerry Meekins, who had purchased a non-refundable ticket between Florida and Atlantic City. The 76-year-old Vietnam veteran and Marine tried to get his $197 back after learning his esophageal cancer was terminal and being told by his doctor not to fly. The decision caused outrage among veterans' groups and the general public, some of whom threatened to boycott Spirit unless both a refund and apology were issued. On May 4, Spirit CEO Ben Baldanza apologized for how the situation was handled and personally refunded Meekins' ticket. Additionally, the airline made a $5000 donation to the Wounded Warrior Project in Meekins' name.

In February 2012, Spirit Airlines established a crew and maintenance base at McCarran International Airport in Las Vegas, Nevada. On December 1, 2012, the airline opened a flight attendant and pilot crew base at Dallas-Fort Worth International Airport.

On Monday, July 1, 2013, a Spirit Airlines jetliner came within two miles of a skydiving aircraft, but was found by the FAA to be in full regulatory compliance. In August 2013, Spirit reached an agreement on a new five-year deal with the Transport Workers Union of America, who represent the airline's flight dispatchers.

On August 7, 2014, Spirit Airlines began new service out of Kansas City, Missouri to five destinations. In November 2014, Morgan Stanley named Spirit the top growth airline pick for investors.

In January 2016, Baldanza stepped down as CEO in order to relocate from Florida, replaced with former Air Tran CEO Robert L. Fornaro. Fornaro has stated that he's interested in merging Spirit with its main rival, Frontier Airlines. If the 2 carriers were to merge, it would create the single largest ultra-low cost carrier in the Americas.

On February 16, 2016, Ned Homfeld, founder of Charter One, which would become Spirit Airlines, died of treatment complications related to leukemia.

In January 2017, Spirit Airlines announced a major expansion into Pittsburgh, which will become the 61st city in the carrier’s network. Spirit’s first Pittsburgh flights launch May 25, when it begins daily service to both Dallas/Fort Worth and Myrtle Beach, S.C. The carrier will add five more routes – to Fort Lauderdale, Houston Bush Intercontinental, Las Vegas, Los Angeles and Orlando – by July 13. Spirit will begin flying from Hartford this year with two routes to Florida and one to Myrtle Beach. Spirit’s first flights from Hartford will begin April 27 when it launches daily flights to Orlando and four-times-a-week service to Myrtle Beach. Daily service to Fort Lauderdale will start June 15. The Florida routes are intended to operate year-round; the South Carolina service will be seasonal.

In September 2017, Spirit temporarily moved their Operations Center from their Fort Lauderdale hub to the Detroit hub, as part of the evacuation for Hurricane Irma.

Spirit follows an ultra low-cost fare model that decouples elements and perks that are often included in the base ticket price of traditional carriers. Passengers who want to customize their itinerary or flight experience pay an add-on fee for each additional feature, which enables the carrier to earn ancillary revenue in excess of 40% of total revenue. These include having an agent print a boarding pass at check-in versus doing it online or at a kiosk, for any large carry-on or checked bags, progressive fees for overweight bags, selected seat assignments, travel insurance, and more.

On October 1, 2007, Spirit began to charge $3 for all drinks. On June 21, 2011, Spirit began charging a $5 fee to passengers who have their boarding passes printed at a check-in desk.

On April 6, 2010, USA Today reported that Spirit would charge for carry-on bags on flights starting August 1, 2010, purchased after April 6, 2010. Bags that fit under the seat and measure 16"x14"x12" are still free but passengers wanting to bring larger bags to put in overhead bins are charged. In October 2011, Spirit reduced the weight limit for checked luggage from 50 pounds per bag to 40 pounds per bag, charging $25 for the first 9 extra pounds, and up to $100 for bags approaching 59 pounds over the 40 pound limit. On June 19, 2014, Spirit Airlines became the first U.S. carrier to temporarily increase their checked baggage fees. The airline increased the checked bag fees by $2 in order to encourage passengers to bring fewer checked bags. For tickets purchased between 6/19/14 through 8/18/14, the first checked bag fee at the airport is $47, the second checked bag is $57.

In 2011, Spirit Airlines became the first U.S. airline to charge passengers for carry-on bags. They were later followed by Allegiant Air and Frontier Airlines.

In May 2013 Spirit airlines dropped its 1-800 number and switched to a Salt Lake city number (area code 801). Its call center is located in Albuquerque, NM and operated by call center company, Sitel.

Spirit currently flies to 61 destinations throughout Central America, the Caribbean, South America, and the United States. As of June 2015, It maintains crew bases at Atlantic City, Chicago–O'Hare, Dallas/Fort Worth, Detroit, Fort Lauderdale, and Las Vegas.

The Spirit Airlines all-Airbus fleet consists of the following aircraft (as of October 2017):

The following aircraft no longer operate in the Spirit Airlines fleet:

In 2006, the airline released a “Hunt for Hoffa” advertising campaign with the tagline “Help us find Hoffa with our Hunt for Hoffa game and enjoy fares from just $39 each way.” The point of the game was to dig for American labor union leader Jimmy Hoffa’s body by clicking grids on the airline’s website, and “winners” were taken to another webpage, saying "You found Hoffa!" thanking them for assisting the National Spirit Sale Center find the union leader’s body. Within hours of the campaign debuting, the airline received a large number of complaints. The promotion was quickly taken down and changed to another promotion, simply titled Happy Sale. This promotion was later listed as #8 on CNN Money’s 101 Dumbest Moments in Business that year.

In December 2007, the airline released a sale with the acronym MILF, standing for “Many Islands, Low Fares.” Online and TV media picked up on this and noted that MILF was popularized in the movie American Pie. This controversy was covered on CBS and ABC News, Countdown with Keith Olbermann, and The O'Reilly Factor.

In April 2008, the airline sent an email to its marketing subscription list announcing “We’re having a threesome. Join us in the fun.” Offering "three sales in one," the email repeatedly proposes the "threesome."

On January 8, the airline reintroduced the MILF Special, described as meaning "Many Islands, Low Fares".

On December 2, shortly after a well publicized car accident involving golfer Tiger Woods, Spirit launched lowered fares in a promotion called the "Eye of the Tiger Sale". Imagery for the campaign featured an SUV crashing into a fire hydrant, with a tiger leaning out the driver's side window.

On February 2, the airline offered the "Many Unbelievably Fantastic Fares (MUFF) to Diving Destinations" promotion. Many of their prominent Caribbean or Floridian destinations were featured.

In June, the airline offered the "Check Out The Oil On Our Beaches" promotion. The ad was in reference to the Deepwater Horizon oil spill, the largest in United States history.

In August, the airline offered the "Don't Be Blue, Slide Down To Low Fares with Double Fisted Savings". The ad was in reference to an incident aboard a JetBlue flight where a flight attendant deployed an emergency slide and left the aircraft with two bottles of beer. Imagery for the ad featured an opened aircraft door and a flight attendant going down an emergency slide with two beer bottles.

On January 12, the airline offered a promotion entitled "Free at Last! Free at Last! Air travel is Free at Last!", which applied for travel the following weekend, celebrating the birthday of Dr. Martin Luther King, Jr.

Spirit made a "Go south" Valentine's Day themed ad showing a woman in a bikini and placed a candy heart with the initial "VD" on her crotch, poking fun at venereal disease.

Shortly afterwards, Spirit made another Valentine's themed ad comparing a diamond ring to vacation packages (while saying "Why not slip her a big package") then showing a gift box directly in front of a man's crotch.

On June 7, amidst the Anthony Weiner Twitter photo scandal, Spirit offered "The Weiner Sale: With Fares Too HARD To Resist." The email promotion included the subject line "Want To See Our Weiner?"

Spirit capitalized on the Summit of the Americas prostitution scandal by featuring an advert with women in pink bikinis, around an agent implying secrecy, and the slogan "More Bang for your Buck" for flights to Cartagena, Colombia – the location of the scandal – as well as other destinations. Colombian officials complained, and Spirit removed the ad after its scheduled 36-hour run.