Route 39 is a 8.15-mile-long (13.12 km) southwest-northeast route through the towns of Harwich, Brewster and Orleans, on Cape Cod, Massachusetts.

It begins and ends at Route 28, acting as a bypass route for those not wishing to follow 28 through Harwich Port and Chatham.

The route begins at Massachusetts 28 in the village of Harwich Port and for its first 1.4 miles (2.3 km), along Sisson Road and a portion of Main Street in Harwich Center, it is coextensive with Route 124.

Route 124 then turns north along Pleasant Lake Ave, leaving the concurrency.

Once it is wholly in Orleans, the road heads north for another 0.3 miles (0.48 km) before terminating at Route 28, approximately 3.5 miles (5.6 km) south of that road's terminus at the traffic circle on the Orleans-Eastham town line.