No, Delta SkyMiles do not expire. Delta Air Lines was one of the first major carriers to implement a permanent "no expiration" policy for its frequent flyer miles, regardless of account activity. This means that even if you do not fly with Delta or use a co-branded credit card for several years, your earned miles will remain in your account indefinitely. This policy stands in contrast to some other international carriers that require at least one qualifying transaction every 12 to 24 months to keep the balance active. While the miles themselves won't disappear, it is important to remember that the "value" of those miles can change over time as the airline adjusts its award redemption charts, and the status of your "Medallion" elite levels still resets annually based on your flying activity within a calendar year.