BC Ferries sail from Sidney, on the Saanich Peninsula, just north of Victoria, to all five of the islands, several times a day; these routes don't take reservations, so arrive early if you're taking a car—45 minutes to an hour early is a good rule of thumb in summer, half an hour in winter. Sailings range from half an hour to more than an hour, depending on stops. Bikes, pets, and foot passengers are welcome. Ferries from the B.C. mainland leave from Tsawwassen, just south of Vancouver. On these routes to and from the mainland, car reservations are highly recommended; for busier sailings, they're required. The ferry journey from Tsawwassen to Salt Spring takes 90 minutes to three hours (depending on the number of intermediate stops), less for the other islands.
Travel between the islands on BC Ferries is possible but generally requires an overnight stay at one of the islands. A fun, low-cost way to cruise the islands is to take one of BC Ferries' Gulf Islands Day Trips—traveling as foot passenger from Swartz Bay, around the islands and back, without disembarking. It's also possible to visit Mayne and Galiano from Salt Spring via water taxi, which doubles as the island school boat.
Salt Spring Island has the most frequent ferry service, and three terminals: ferries from Swartz Bay, near Victoria, arrive at Fulford Harbour, on the southern tip of the island, 20 miles from Ganges, the main town. Ferries from the B.C. mainland arrive at Long Harbour, on the island's east coast, closer to Ganges. Salt Spring also has BC Ferry service from the Cowichan Valley, with sailings every hour or so from Crofton, 20 minutes north of Duncan, to Vesuvius Bay on Salt Spring. A BC Transit minibus runs from all three ferry terminals to the town of Ganges, but it doesn't meet every ferry; check online schedules first. For a taxi on Salt Spring, call Silver Shadow Taxi.
Transport on the other islands is limited: Pender has the Pender Island Cab Company. Most island accommodations collect guests from the ferry terminal if asked. Cycling is popular on the islands, despite the hilly terrain.