Highway 84 in the U.S. State of Montana is a route running easterly from the small community of Norris to an intersection with U.S. Route 191 north of Bozeman Hot Springs, a distance of approximately 29 miles (47 km). The highway's eastern terminus, about 7 miles (11 km) west of Bozeman, is a location known locally as "Four Corners." From Four Corners, US 191 runs east to Bozeman, and south to West Yellowstone; Highway 84 travels west to Norris; and Montana Highway 85 runs north to Belgrade.

Before receiving its current designation, Highway 84 was designated as Montana Secondary Highway 289.