Most major American airlines allow you to check in online, including Delta Airlines, American Airlines and Southwest Airlines. Other airlines with online check-in include United Airlines, U.S. Airways, Frontier Airlines and Jet Blue.
Online check-in enables you to check in and print your boarding passes at home. Airlines that support mobile boarding passes, such as United Airlines and American Airlines, allow customers to download boarding passes to a phone or tablet. Digital boarding passes are not be available for all airports.
By checking in online, you have the option to skip long lines at airport counters. If you fly with carry-on baggage, simply move directly to security lines. If you have baggage to check, you must drop it off at a bag-drop counter.
Most airlines offer online check-in as early as 24 hours before the flight departs. Look in your email for a direct link to the check-in page, or visit the airline's website. The check-in page of an airline's website usually requires you to enter your reservation number and last name.
During the check-in process, most airlines offer the opportunity for travelers to choose or change seats. On airlines such as Southwest, which allocates boarding order on a first-come, first-serve basis, early online check-in gets you on the plane faster.