The largest island in the archipelago, San Juan Island is about 20 miles long and seven miles wide, covering 55 square miles. Picturesque Friday Harbor sits along the west side, its marina protected by Brown Island. Acting as the county seat, Friday Harbor is the only incorporated town in the islands and is the commercial center of the San Juans. It is a U.S. Customs port of entry, as is Roche Harbor  on the other side of the island.
Warning: Friday Harbor has a big parking problem in the summer, and the city strictly enforces a two-hour downtown parking limit. Get back to your car three minutes late and you'll probably have a ticket pasted on the windshield.
The Washington State Ferry (206/464-6400, www.wsdot.wa.gov/ferries ) stops right in Friday Harbor on San Juan Island. In the summer, ferries leave Anacortes  at least a dozen times a day 4:30 a.m.–12:20 a.m.; nearly all of them stop at Friday Harbor. See the Getting to the San Juan Islands  information for details on ferry service (including private ferries) and scheduled flights to San Juan Island.
You don't need a car on San Juan Island. San Juan Transit & Tours (360/378-8887 or 800/887-8387, www.sanjuantransit.com ) operates shuttle buses between Friday Harbor and Roche Harbor , with stops at Lakedale, Lime Kiln State Park, San Juan County Park, Mitchell Bay, and English Bay. Unfortunately, they do not run to the south end of the island (American Camp ). Buses operate May–September, and service is daily in summer and weekends only until mid-May. The cost is a reasonable $5 one-way, $10 round-trip, or $15 for an all-day pass, and buses can carry bikes and luggage. The office is next to the Friday Harbor ferry in the Cannery Landing Building.
If you must have your own set of wheels, M&W Auto Rentals (360/378-2886 or 800/323-6037, www.sanjuanauto.com/rental.html , $50–70 per day) offers a range of vehicles for rent, including two- and four-door sedans, convertibles, SUVs, and large passenger vans.
Susie’s Moped and Car Rentals (360/378-5244 or 800/532-0087, www.susiesmopeds.com .) also rents tiny Geo Trackers from its shop at the top of the ferry lanes in Friday Harbor, in addition to bikes and mopeds.
Call Bob’s Taxi & Tours (360/378-6777 or 877/482-9426) for local rides year-round. Friday Harbor to Roche Harbor  is around $22 for two people.