The Island Explorer is a seasonal bus system that provides fare-free transportation on and near Mount Desert Island in the U.S. state of Maine. It is operated by Downeast Transportation, and largely intended to serve visitors to Acadia National Park as a means to reduce area traffic within the park and in area communities, including the Schoodic Peninsula. It typically runs from mid-June through the beginning of October. Operations began in 1999, and in 2019 the service carried over 647,000 passengers.