Delta Air Lines operates its main hub at Hartsfield-Jackson Atlanta International Airport, the busiest airport in the world. The airline's loyalty program, SkyMiles, is a dollar-based program that allows you to earn miles without having to fly; enrolling in the SkyMiles program is free of cost. While the most popular way to earn miles is using Delta SkyMiles American Express Card (Amex), users can link their SkyMiles account to other partner programs and earn points and medallion status. Earn miles with SkyMiles on everyday purchases without even stepping foot on a plane. These miles can be used for travel on any Delta Air Lines flight or Delta Vacations package or for rewards like upgrades and premium drinks at Delta Sky Club. Frequent flyers can get closer to their next destination with each trip and purchase.