SkyMiles is the frequent-flyer program of Delta Air Lines that offers points (or "miles") to passengers traveling on most fare types, as well as to consumers who utilize Delta co-branded credit cards, which accumulate towards free awards such as airline tickets, business and first-class upgrades, and luxury products. Created in 1981 as the "Delta Air Lines Frequent Flyer Program", its name was changed to SkyMiles in 1995. Originally all airlines including Delta, only gave miles for airline travel and not credit card expenditures. Delta claims to have been the first major U.S. airline without mileage expiration, so travelers can redeem awards at their leisure, but others have since followed. The airline also has a separate SkyBonus program that provides small to mid-sized business owners with a way to earn points for trips taken by employees, good towards free flights, upgrades, Medallion status and other travel awards. It has been ranked fairly high according to some independent news outlets.

In addition to its Delta Connection, Delta Shuttle and SkyTeam alliance partnerships, Delta offers frequent flyer partnerships with the following airlines:

In addition to the air miles, SkyMiles can be redeemed and even earned on SkyMiles cruises but that is actually a separate company. Miles may be used and accrued on Delta Vacations but that is also a separate company although Delta is the parent company.

Delta offers four published tiers of elite status within the SkyMiles program. These are known as Medallion statuses and previously were achieved by flying a certain number of Medallion Qualification Miles (MQM) or Medallion Qualification Segments (MQS) between January 1 and December 31 each year. Beginning in 2014, a certain number of Medallion Qualification Dollars (MQD) was required for the US members in addition to either the MQM or the MQS requirement.^{[citation needed]}

In September 2023, Delta announced a major change in how Medallion status would be earned beginning in 2024 (earning for status in 2025). MQM and MQS were abolished in favor of a simpler structure relying only on MQD to earn status, and new ways to earn MQD were created, including spending on the co-branded SkyMiles American Express credit cards.

Delta Private Jets Card holders receive Diamond Medallion tier status.

Medallion status entitles members to unlimited complimentary upgrades, subject to availability, on most published economy fares on Delta and certain Delta-designated codeshare flights in North America within or between the United States (excluding Hawaii) and Bermuda, Canada, Central and South America, the Caribbean and Mexico. In addition, preferred coach seating such as in the Economy Comfort section is set aside for medallion members for when first and business class upgrades are not available. Although not a published benefit, certain top tier members of the program have been transferred at Delta hubs by an automobile and chauffeur pick up service (see photograph). There is also a Delta 360 level of status which is awarded by invite only to their very best customers. How to earn this status has not been published. There have been further updates in the wake of the COVID-19 pandemic.

In 1991, Delta acquired most of the assets of Pan Am Airways, and in November 1991 all members of the Pan Am frequent flyer program, WorldPass, were transferred to Delta's FF program, with their accumulated miles.