Southeast Michigan, also called southeastern Michigan, is a region in the Lower Peninsula of Michigan that is home to a majority of the state's businesses and industries as well as slightly over half of the state's population, most of whom are concentrated in Metro Detroit.

The Lower Peninsula of Michigan – also known as Lower Michigan – is the larger, southern and less elevated of the two major landmasses that make up the U.S. state of Michigan; the other being the Upper Peninsula, which is separated by the Straits of Mackinac. It is surrounded by water on all sides except its southern border, which it shares with Indiana and Ohio. Although the Upper Peninsula is commonly referred to as "the U.P.", it is uncommon for the Lower Peninsula to be called "the L.P."