Intrastate airlines in the United States were air carriers operating solely within a single US state and taking other steps to minimize participation in interstate commerce, thus enabling them to escape tight Federal economic airline regulation prior to US airline deregulation in 1979. These intrastate carriers therefore amounted to a small unregulated, or less regulated, sector within what was otherwise then a tightly regulated industry. Geography alone did not determine intrastate status.

Southwest Airlines Co. is a major airline in the United States that operates on a low-cost carrier model. It is headquartered in Love Field, Dallas, Texas, within the Dallas–Fort Worth metroplex, and has scheduled service to 121 destinations in the United States and 10 additional countries. As of 2018, Southwest carried more domestic passengers than any other United States airline. It is currently the third largest airline in North America based on passengers flown.