Heading north from Ios to Paros is one of the standard moves in a central Cyclades trip. Ios is small and focused, known for its beaches and its lively hilltop Chora, while Paros is bigger and more varied, with its capital Parikia, the harbour village of Naoussa, long beaches and ferries to almost everywhere. Many travellers spend a few nights on Ios, then move up to Paros to slow down or to connect onwards.
The crossing is short and well served. Blue Star Ferries carries the route all year on its conventional ships, and from late spring to autumn Seajets and Golden Star Ferries add high-speed boats that cut the time to about an hour. You leave from the harbour at Ormos on the west side of Ios, a short ride below Chora, and arrive in Parikia, where the ferry quay is at the edge of town.
The big decision is price against time. The Blue Star fare can be a fraction of the high-speed fare: in Ferryhopper's data the conventional ship started at €9.50, the fast boats at €63.50 to €63.70. The slower ship takes about twice as long, but it is roomier, has open decks and makes sense if you are carrying a lot of luggage or a car.
Paros is also a good place to end a trip. It has an airport (PAS), boats to Piraeus all year and to Rafina in season, so if you are flying home from Athens, Ios to Paros can be the first leg of a gentle journey back rather than one long day at sea.