* Interstate 90 (I-90): This is the longest interstate highway in the United States, running from Seattle, Washington, to Boston, Massachusetts. In Montana, it runs through the heart of the state, connecting major cities like Billings, Butte, and Missoula.

* Interstate 15 (I-15): This interstate runs from San Diego, California, to Sweetgrass, Montana, on the Canadian border. In Montana, it travels through the western part of the state, passing through cities like Bozeman and Great Falls.

These two interstates are crucial for transportation in Montana, connecting major cities and facilitating commerce and tourism throughout the state.