The oldest airline still operating in the United States, Delta conducts more than 4,000 flights a day to 280 destinations on six continents. It's headquartered at Hartsfield-Jackson Atlanta International Airport, where it’s responsible for the majority of the approximately 104 million passengers who travel through the world’s busiest airport each year. Delta pioneered the hub-and-spoke system that’s now a common organizational model for many airlines. Ahead, find what you need to know about traveling on Delta Air Lines.