M-37 is a north–south state trunkline highway in the US state of Michigan. The southern terminus is near the border between Kalamazoo and Calhoun counties at exit 92 of Interstate 94 (I-94) southwest of Battle Creek. The northern terminus is at the Mission Point Light on Old Mission Point in Grand Traverse County. In between, the highway connects Battle Creek, Grand Rapids, and Traverse City. Motorists will travel through agricultural land, forests, suburbs, and large cities along the way. The section of M-37 on the Old Mission Peninsula was designated what is now a Pure Michigan Scenic Byway in 2008.

Originally named the Muskegon, Grand Traverse and Northport State Road, and later the Newaygo and Northport State Road, today's modern highway can be traced back to the 19th century and earlier. The southernmost section between Grand Rapids and Battle Creek parallels an early Indian trail. The modern highway was formed by July 1, 1919, along this segment. By the 1940s, a second section of highway was designated M-37, creating a gap between it and the original section. This gap was eliminated in the 1950s, completing the M-37 corridor in the state. Additional changes to the routing were made through the Grand Rapids area into the 1970s.

M-37 runs for 221.27 miles (356.10 km) through the western side of the Lower Peninsula of Michigan, connecting Battle Creek, Grand Rapids, and Traverse City. Segments of it have been listed on the National Highway System (NHS), a network of roads important to the nation's economy, defense, and mobility. Through the Grand Rapids area, M-37 is on the NHS along Broadmoor and East Beltline avenues north of M-6 and the concurrency with I-96. The second segment on the NHS runs from M-115 in Mesick to Traverse City. The road has also been designated what is now a Pure Michigan Byway through the Old Mission Peninsula. The trunkline is maintained by the Michigan Department of Transportation (MDOT). As part of this responsibility, the department tracks the traffic volumes along M-37. MDOT uses a metric called average annual daily traffic, which is a calculation of the average traffic level for a segment of roadway on any average day of the year. Along M-37, the volume varies from the peak 49,173 vehicles on a section of I-96/M-37 in Grand Rapids to the 718 vehicles at the northern terminus by the Mission Point Light.

M-37 starts joined with Business Loop I-94 (BL I-94) as the two highway designations run concurrently at exit 92 on I-94 southwest of Battle Creek. They follow Columbia Avenue and pass around the southern side of the W. K. Kellogg Airport. When the roadway meets M-96, BL I-94/M-37 turns northward, joining M-96 around the eastern end of the airport to Dickman Road. M-37 jogs westerly onto Dickman Road before continuing northward on Helmer Road through suburban residential areas in Springfield and across the Kalamazoo River into Level Park-Oak Park. There, the highway intersects M-89, passes through more residential areas, and exits the Battle Creek metro area.

North of Bedford, M-37 meanders through rural Barry County. The road passes through mixed agricultural and forest lands near several small lakes in the area. On its path to Hastings, the trunkline runs through Dowling and meets the western terminus of M-79. The highway follows Hanover Street through the south side of Hastings into downtown, where it turns west on Green Street and north on Broadway Street. At the intersection of Broadway and State streets, M-37 meets and joins M-43. West of Hastings, M-43 separates and heads south toward Kalamazoo while M-37 turns northwesterly and runs parallel to the Thornapple River. The highway follows the river west and north to the community of Middleville through mixed farms and forests.

In southern Kent County, M-37 follows Cherry Valley Road through Caledonia. As the highway transitions to Broadmoor Avenue, the landscape also transitions from rural to suburban. North of 76th Street, Broadmoor widens to a four-lane boulevard which passes a campus of Davenport University near the M-6 freeway on the outskirts of the Grand Rapids area. This section is dominated by light industrial complexes west of the Gerald R. Ford International Airport in the suburb of Kentwood. These complexes change over to retail establishments north of 32nd Street. At 28th Street, Broadmoor Avenue ends, and East Beltline Avenue begins. M-37 follows East Beltline Avenue between the Woodland Mall and the Centerpointe Mall. North of the malls, M-37 passes through the campus of Calvin University and along residential areas at the east end of Reeds Lake. The intersection of East Beltine Avenue and Fulton Street is the western terminus for M-21, a highway that runs east across the state to Flint. North of this junction, M-37 meets I-96 and M-44

M-37 parts East Beltline Avenue and turns west along I-96. The freeway runs west and then north around the edge of Grand Rapids. Near 3 Mile Road, I-96/M-37 runs west again, continuing across the Grand River and meeting the US Highway 131 (US 131) freeway. The next interchange immediately west of US 131 is for Alpine Avenue, which M-37 follows north. This road runs through a commercial and retail corridor in the communities of Walker and Comstock Park. South of 6 Mile Road, Alpine Avenue widens into a four-lane divided highway. This highway splits from Alpine Avenue north of 8 Mile Road and turns to the northwest as the surroundings transition to rural farmland again. M-37 transitions back to a two-lane road south of Sparta. The trunkline passes to the west of Kent City and crosses into Muskegon County at Casnovia. Through this area, the highway parallels a line of the Marquette Rail that runs north from Grand Rapids.

West of the county line, M-37 meets and merges with M-46 along Apple Avenue. The two highways separate at a roundabout junction where M-37 turns north on Newaygo Road. M-37 passes Half Moon Lake and through Bailey. In recent years the highway has served as the location of West Michigan's Longest Yard Sale which spans about 75 miles (121 km) of the route starting in the Bailey–Grant area of Newaygo County through northern Lake County. Between |Grant and Newaygo, the farms transition to forest. M-82 follows M-37 through downtown and across the Muskegon River. The highway continues north along Evergreen Drive between Emerald, Sylvan, and Twinwood lakes. This area is where M-37 crosses into the Manistee National Forest. M-20 follows M-37 through downtown White Cloud and over the White River. Further north, the road passes through Brohman and Lilley in the northern end of the county.