Atlantic Southeast Airlines (ASA) was an American airline based in the A-Tech Center in College Park, Georgia, flying to 144 destinations as a Delta Connection carrier and, as of February 2010, commenced service as a United Express carrier. It was a wholly owned subsidiary of SkyWest, Inc. ASA operated nearly 900 flights each day. Its main hub was at Hartsfield-Jackson Atlanta International Airport (ATL). ASA changed its name to ExpressJet in 2011.

In November 2011, ASA and ExpressJet received a single operating certificate from the FAA and in December 2011, all flights were then operated by ExpressJet on behalf of its major airline code sharing partners.

On March 12, 1979, the company was incorporated as Atlantic Southeast Airlines, Inc. with headquarters established in the Atlanta area. June 27 saw the start of operations with one 19-passenger de Havilland Canada DHC-6 Twin Otter turboprop aircraft between Atlanta and Columbus, Georgia. From 1979 to 1999 the call sign for ASA was "ACEY". In 1999 there was confusion with call sign for the Federal Aviation Administration (FAA)- New Mexico based fighter unit with the call sign "ACER". The FAA insisted one change call its sign and ASA was the one to change since they had used the call sign for the least amount of time. June 27, 1999 ASA changed to call sign CAA "Candler" after the founder of Coca-Cola, Asa Candler. On March 15, 2006 ASA was allowed to change its call sign back to ACEY, after the New Mexico fighter unit went defunct. Over the years, ASA's ICAO identifier changed from ASE to CAA to ACY to ASQ.. The company went public when the initial stock offering was completed in 1982.

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