Colfax Avenue is the main street that runs east–west through the Denver-Aurora metropolitan area in Colorado. As U.S. Highway 40, it was one of two principal highways serving Denver before the Interstate Highway System was constructed. In the local street system, it lies 15 blocks north of the zero meridian (Ellsworth Avenue, one block south of 1st Avenue), and would thus otherwise be known as 15th Avenue. The street was named for the 19th-century politician Schuyler Colfax. From west to east, it starts at Heritage Road in Golden as U.S. Highway 40 and the Business Route of I-70, and continues east through Lakewood and enters Denver at Sheridan Boulevard. U.S. Highway 287 is routed along Colfax Avenue as well, which continues east through Denver and Aurora. In the eastern outskirts of Aurora, Colfax Avenue meets I-70 and the two U.S. highways follow the I-70 route eastward; signage at Picadilly Road and frontage road the frontage road is labeled Colfax Avenue; while appearing to be interrupted at the I-70 and Colfax Avenue interchange; Colfax Avenue has signage in the complex E-470 interchange, appearing as a frontage road of I-70 on most maps; this frontage road starts just west of the Colfax Avenue and I-70 interchange, and at an interchange (I-70 Exit 292), Colfax Avenue becomes State Highway 36 and continues east from Aurora through Bennett to end at Headlight Road in Strasburg.

Colfax Avenue cuts through Original Auraria, the city's historic core, and skirts the southern edge of downtown Denver. Because of the dense, mixed-use character of the development along Colfax Avenue, the Regional Transportation District bus route 15 - East Colfax has the highest ridership in the RTD system. In 2006, the first Colorado Colfax Marathon was held, traversing the length of Colfax Avenue through the three cities.

It's become legend that Playboy magazine once called Colfax "the longest, wickedest street in America," but attempts to source the actual quote have failed. However, such activities are actually isolated to short stretches of the 26-mile (42 km) length of the street. Periodically, Colfax undergoes redevelopment by the municipalities along its course that bring in new housing, businesses and restaurants. Some say that these new developments detract from the character of Colfax, while others worry that they cause gentrification and bring increased traffic to the area.