Lake Michigan is one of the five Great Lakes of North America, and the second largest lake by volume. To the east, its basin is conjoined with that of Lake Huron through the wide and deep Straits of Mackinac, giving it the same surface elevation as its easterly counterpart; hydrologically, the two bodies are a single lake that is, by area, the largest freshwater lake in the world.

Lake Michigan is the only Great Lake located fully in the United States, the other four are shared between the U.S. and Canada. It is the world's largest lake, by area, located fully in one country, and is shared, from west to east, by the U.S. states of Wisconsin, Illinois, Indiana, and Michigan. Ports along its shores include Chicago, Illinois, Gary, Indiana, Milwaukee and Green Bay, Wisconsin, and Muskegon, Michigan.

To the north, the lake is flanked by long bays, including Green Bay in the north-west, and Grand Traverse and Little Traverse bays in the north-east.

The word Michigan is believed to come from the Ojibwe michi-gami or mishigami, meaning "great water"