Aegean Airlines offers online check-in starting 48 hours before departure and closing 30 minutes prior to the scheduled departure time. To check in, visit the Aegean Airlines website or use their mobile app. You'll need your booking reference and last name. During online check-in, you can select seats and obtain a digital boarding pass. If you have checked baggage, you must drop it off at the designated counters before the cutoff time. It's advisable to arrive at the airport early to ensure a smooth check-in process.