Only two ferry operators serve Astypalea.
In summer, Blue Star Ferries arrive at the 'new port' which is rather isolated at Agios Andreas, 6.5km north of Pera Gialos. A bus is scheduled to meet each boat, as are the island's two taxis. Astypalea Tours will transfer you for €5. Outside high season, however, inconveniently, the ferry arrives in the dead of night, so book your transfer ahead if your accommodation doesn't meet you.
One ferry arrives around four times weekly, having sailed from Piraeus (€38.50, 9¾ hours) via Paros (€37, 5¼ hours) and Naxos (€20, four hours), and sets off back along the same route. The other stops once per week between Piraeus and Rhodes, calling also at Kalymnos (€14.50, two hours), Kos (€17, three hours), Tilos (€15.50, six hours) and Nisyros (€12.50, five hours).
Nisos Kalymnos (www.anekalymnou.gr) connects Pera Gialos' small harbour (sometimes referred to as the Skala Port) twice weekly with Kalymnos.