The largest airlines in the world can be defined in several ways. As of 2023, Delta Air Lines is the largest by revenue, assets value, fleet size, and market capitalization; American Airlines Group by passengers carried, revenue passenger mile, number of employees and destinations served; FedEx Express by freight tonne-kilometers; Ryanair by number of routes; and Turkish Airlines by number of countries served.

Delta Air Lines is one of the major airlines of the United States and a legacy carrier headquartered in Atlanta, Georgia. The United States' oldest operating airline and the seventh-oldest operating worldwide, Delta along with its subsidiaries and regional affiliates, including Delta Connection, operates over 5,400 flights daily and serves 325 destinations in 52 countries on six continents. Delta is a founding member of the SkyTeam airline alliance. As of the end of 2022, it had 90,000 employees.