Giannutri is connected by regular ferry to Porto Santo Stefano, in the Argentario peninsula. MareGiglio, based in Isola del Giglio, Via Umberto 1 (tel. 0564/812920; www.maregiglio.it), runs the boats. Tickets are 13€ each way and the journey takes about an hour. In summer, there are daily departures from Porto Santo Stefano at 10 or 10:30am. (The return boats from Giannutri leave at 4:30pm.) In May, September, and October, there are four to six boats per week (always with weekend service), usually leaving Porto Santo Stefano at 10am. From November to March, service is greatly reduced, with only a few boats per week to Giannutri.
Though they aren't an official transportation link, there are private excursion boats at least once per day in summer from Giglio Porto on Isola del Giglio to Giannutri (a short trip of about 45 min.). In fact, Giannutri is more commonly visited as a day trip from Giglio than from Porto Santo Stefano. Vegastar (tel. 335/7589445; www.veganavi.it) operates connections between Giannutri and Giglio as well as Porto Santo Stefano. Ferries (15€-20€ one-way) run daily from mid-June to mid-September and several times per week from the Easter period through mid-October. Service is suspended the rest of the year.
Note that from mid-May through the end of October on Giannutri, the National Park service imposes an island entrance fee and a limit on the number of visitors allowed on Giannutri at any given time -- a maximum of 300 persons per day. To visit certain protected land zones, even more restrictions apply: You must go with a guide in groups of no more than 25 persons.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.