Route 84 is a highway in the Missouri bootheel. It starts at the Arkansas state line west of Kennett and ends at Interstate 155/U.S. Route 412 south of Caruthersville.

Arkansas Highway 90 crosses into Missouri at Kennett and proceeds eastward. It crosses through the center of the city, passing north of the Kennett Memorial Airfield. Roughly 5 miles into its course, Route 84 becomes concurrent with US 412. The two highways serve as the southern terminus of Route 25 and, in Bragg City, parallel the southern border of the Little River Conservation Area. The roads remain concurrent until Hayti, when US 412 splits off to the southeast. Route 84 intersects a concurrency between US 61 and I-55 as it also turns towards the southeast.

As the highway approaches the Missouri River and enters Caruthersville, it turns southward. It ultimately ends at I-155/US 412. Route 84's 30.1-mile path is located entirely within the Bootheel region and spans two counties: Dunklin and Pemiscot.

Between 1976 and 1977, the east end of Route 84 was extended slightly to meet I-155. US 412, and by extension its concurrency with Route 84, came into being in the area by 1986.