Hydrofoils and ferries are the most likely way of getting to the islands. Note that services departing to/from Positano and Amalfi operate solely from around May to September or October. At other times of the year, you will have to catch services from Naples or Sorrento. In Naples, hydrofoils leave from Molo Beverello, with slower ferries leaving from the adjacent Calata Porta Massa. Generally, there is no need to book: just turn up around 35 minutes before departure in case there's a queue.
Ischia's main ferry terminal is in Ischia Porto. However, there are also other smaller terminals in Casamicciola and Forio.
Caremar Operates up to six daily hydrofoils from Naples to Ischia Porto (€17.90, 45 minutes) and Procida (€8.70, 20 minutes), as well as ferries.
Alilauro Operates hydrofoils from Naples to Ischia Porto (€20.10, 50 minutes, up to 12 daily) and up to six hydrofoils daily between Forio and Naples (€21.50). There are also two daily ferries to Sorrento (€22.90, one hour) from Ischia Porto.
SNAV Operates hydrofoils from Naples to the Ischian town of Casamicciola (€20.20 to €21.20, one hour, five daily).