Public transportation in Maine is available for all four main modes of transport—air, bus, ferry and rail—assisting residents and visitors without their own vehicle to travel around much of Maine's 31,000 square miles (80,000 km2).

The Greater Portland METRO is a regional public transportation system, established in 1966, in Southern Maine. Operated by the Greater Portland Transit District, a transit district comprising Portland, Westbrook, Falmouth, Yarmouth, Freeport, and Brunswick, the system also covers Gorham and The Maine Mall portion of South Portland.