U.S. Route 36 is a major east–west route in the U.S. state of Colorado, extending from Rocky Mountain National Park to the Kansas state line.

US Route 36 begins at Deer Ridge Junction in Rocky Mountain National Park, where it intersects US Route 34 (Trail Ridge Road) on the eastern slope of the Rocky Mountains. It exits the park at the Beaver Meadows Visitor Center and enters the town of Estes Park, where it is briefly overlapped with Business US 34 until it meets (but does not cross) the main US 34 again at an intersection shaped like the letter K. On its way out of Estes Park it intersects SH 7 at South St. Vrain Avenue, for the first of three times.

It then descends southeast through North St. Vrain Canyon to the town of Lyons, which it enters on Main Street. At 5th Avenue in Lyons, it intersects SH 7 again, beginning an overlap to Boulder which is signed only as US 36. At 5th Avenue and Main Street in Lyons, it divides into a pair of one way streets with the eastbound direction traveling one block south on 5th Avenue and turning east onto Broadway Street, and the westbound direction using Main Street. The two directions reunite in two blocks and leave Lyons southeastward as four-lane Ute Highway. Just outside of Lyons, US 36 turns south at a signalized intersection onto two-lane North Foothills Highway, while SH 66 continues east to Longmont. From Lyons to Boulder, US 36 pretty much traces the edge of the foothills.

US 36 enters Boulder on four-lane-wide 28th Street, where it serves the city's main shopping area. On the north side of Boulder, it intersects SH 119 at Diagonal Highway, beginning a 1.4 mile overlap that extends until SH 119 turns west onto Canyon Boulevard towards Nederland. One block farther south, SH 7 diverges from its overlap with US 36 by turning east onto Arapahoe Avenue. Leaving the Boulder shopping district, US 36 crosses Boulder Creek and passes through the University of Colorado campus area as an expressway to the interchange with Baseline Road, where it meets Spur US 36, a two-block long connector along 27th Way to SH 93, signed only as "To SH 93" and "To US 36".

Just after the Baseline Road interchange, which was formerly a diamond interchange but has since become a one-quarter cloverleaf, US 36 curves to the southeast. At this point the stretch of US-36 called the Denver-Boulder Turnpike begins, since this portion was a toll road from its opening in 1952 until 1967, when the toll was lifted.

The road intersects SH 157, termed Foothills Parkway in the Boulder street system, on its way out of town. Northwestbound traffic approaching Boulder on the turnpike can stop at a scenic overlook on a high hill, providing a panoramic view of the Front Range mountains, the City of Boulder, and its famous Flatirons rock formation; a monument to the Denver-Boulder Turnpike's original builders is also located here. Continuing southeast, the road enters the fast growing Denver suburbs of Broomfield and Westminster, which have become popular locations for High-Tech businesses, which can be seen lining the turnpike. An interchange at 96th Street provides access to the Northwest Parkway and thereby to the E 470 outer beltway around Denver. At an interchange with SH 121 and SH 128 in Broomfield, it meets (but does not cross) US Route 287. It then has another interchange with US 287 again at Federal Boulevard near 76th Avenue in Westminster. The interchange at 76th and Federal was the terminus of the Denver-Boulder Turnpike when it was still a toll road, but in common parlance the Turnpike now extends all the way east to I-25.

At the very complicated junction of US-36, I-25, I-76, and I-270, US-36 emerges overlapped and unsigned with I-270, and continues overlapped and unsigned with I-70 when I-270 ends near the former Stapleton Airport site. At Colfax Avenue, this I-70/US 36 overlap is also joined by US-287 (again) and US-40. From the interchange with Colfax Avenue, the road continues to Watkins and then to Byers, unsigned in its four-way multiplex with I-70, US-40, and US-287. The former route through Bennett, Strasburg, and Byers is signed separately as Colorado State Highway 36.

At Byers, US 36 heads eastward on its own as a separate rural highway, while the I-70/US-40/US-287 multiplex curves to the southeast. US 36 passes through several very small settlements including Last Chance, Lindon, Anton, and Cope in Washington County and Joes and Idalia in Yuma County. Many of the towns on this desolate 105-mile (169 km) section of highway are so small they do not provide basic traveler services such as gasoline, and winter drivers are cautioned by signs that there is no snowplowing at night. At Cope, it is joined by SH 59 for about 6 miles (9.7 km). In Yuma County, near Idalia, it jogs north, becoming concurrent with US 385 for about 3 miles (4.8 km) before turning east again and continuing about 10 miles (16 km) to the Kansas border.

The portion of US Route 36 within Rocky Mountain National Park is a toll road, requiring a park entrance fee.

US Route 36 is a freeway from Boulder to Byers, portions overlapped with I-270 and I-70.

US 36 was extended westward in stages into Colorado beginning in 1930. By 1946, it had reached downtown Denver. It was fully paved by 1950.

The Denver-Boulder Turnpike was championed by business and university interests in Boulder due to there being no direct route between Denver and Boulder. It opened in 1952 with the toll being $0.25. Its southeastern end was originally at US 287 Federal Boulevard, but when Denver's new Valley Highway (now I-25) was built, the two roads were connected in 1956 by 2-mile (3.2 km) long SH-382, which has always been commonly regarded as a portion of the Turnpike. When the bonds for the Turnpike were paid off ahead of time in 1967, US 36 was extended from Colfax Avenue in Denver along I-25, SH-382, the newly-free turnpike, SH-7, and SH-66, to end at US 34 in Estes Park. Eventually these portions that overlapped previous state highways became signed only as US 36.

In 1976, US 36 through Denver was straightened to use I-70, I-270, I-76, and I-25. By 1978, US 36 had been further extended west from Estes Park along SH-66 to end inside Rocky Mountain National Park at a second intersection with US 34. In 2003, the overlap with I-76 and I-25 was eliminated when I-270 was extended to I-25 and the Turnpike.