Mackinac Island is accessible only by ferry or small plane — no bridge connects it to the mainland. Two ferry companies, Shepler's and Arnold Line, operate competing services from two mainland ports: Mackinaw City on the southern shore of the Straits and St. Ignace on the northern shore. Both crossings take about 15–20 minutes; ferries run multiple times daily from May through October, with reduced frequency in the shoulder season. St. Ignace is the closer of the two ports if you're coming from the Upper Peninsula; Mackinaw City is more convenient from the south.
No private motor vehicles are permitted on the island. You cannot drive a car onto the ferry — leave your vehicle in one of the parking lots at the mainland ferry terminals. The island has its own small airport (Y83) for those arriving by small plane, typically charter or private aircraft.