Mesa Airlines, Inc. is an American regional airline based in Phoenix, Arizona. It is a FAA Part 121 certificated air carrier operating under air carrier certificate number MASA036A issued on June 29, 1979. It is a subsidiary of Mesa Air Group. It was known briefly as Mountain West Airlines from 1995 to 1996. It operates flights as United Express, US Airways Express, and under the brand go! Mokulele for flights within the Hawaiian Islands. It serves more than 180 markets in the Western Hemisphere. Mesa's safety record was noted as having the fewest incidents among domestic regional airlines in the Journal of Air Transportation. In March 2011, Mesa emerged from Chapter 11 bankruptcy. Mesa filed for Chapter 11 in January 10, hoping to shed financial obligations for leases on airplanes it no longer needs. The time that Mesa spent in bankruptcy was one of the shortest time periods in aviation history.

Mesa Airlines operates as:

From 1989 to 1998, Mesa Airlines operated as a conglomeration of up to eight separate airlines. For the history of the acquisition and expansion of Mesa Airlines during this time frame see Mesa Air Group. The following history section details the history of the individual airlines that comprised Mesa Airlines during this time frame: