Route 63 is a secondary state highway in the U.S. state of Connecticut, from New Haven up to Canaan, running for 52.57 miles (84.60 km). It connects the Greater New Haven area to Northwestern Connecticut via the western suburbs of Waterbury.

Route 63 is mostly a 2-lane surface road with occasional 4-lane sections. There is also a partially controlled access (non-freeway) section in Middlebury. Route 63 is a principal arterial road between New Haven and Watertown. From Watertown to Litchfield, Route 63 is a minor arterial road, and from Litchfield to Canaan, it is a small, rural collector road. One of the most congested points in the Waterbury area is the intersection with Route 64 in Middlebury.[citation needed]

A 3.4-mile (5.5 km) section of the road in Litchfield is a designated state scenic road.

Route 63 was designated in 1932 and originally connected Morris to Woodbridge using the alignment of the Straits Turnpike, an early 19th-century toll road connecting New Haven to Litchfield. Route 63 is still locally called the Straits Tunrpike in Middlebury and Watertown. In the mid-1940s, Route 61 between Morris and Cornwall was reassigned to an extended Route 63. Another extension happened in the 1952 when Route 63 took over part of Route 43 from Cornwall to Canaan where it ends today. Between 1954 and 1976, Route 63 extended south to US 1 via an overlap with Route 10.