Yes, Greek ferries can and do book out during the peak summer months of July and August, as well as during major holidays like Orthodox Easter and the August 15th long weekend. While large "conventional" ferries (like Blue Star) rarely sell out of "Deck" or "Economy" tickets, cabins and vehicle spots on these ships often sell out months in advance. For the faster High-Speed Ferries (like SeaJets), which have a much more limited seating capacity and strictly assigned seats, tickets can vanish quickly for popular routes like Athens to Mykonos or Santorini to Crete. In 2026, most travelers use e-tickets and mobile boarding passes, making the booking process much faster. If you are traveling in the "shoulder season" (May, June, September), you can usually book a few days in advance or even at the port. However, for a stress-free summer island-hopping adventure, it is highly recommended to book your ferry tickets at least 2 to 3 months out to ensure you get your preferred departure time and seating class.