Frontier Airlines is one of the largest low-cost airlines based in the US, headquartered in Denver, Colorado. It was founded in 1994, and today operates flights to more than 100 cities across the country, as well as a growing number of international destinations across Central American and the Caribbean. Staying true to its image as a budget airline, Frontier doesn’t offer any business class or first class seats on any of its flights. It does, however, offer frequent fliers the chance to rack up air miles and gain rewards thanks to its FRONTIER Miles program, which rewards you with one air mile for each mile flown.