Colorado Boulevard (or Colorado Street in Glendale and parts of Arcadia) is a major east–west street in Los Angeles County, California, United States. It runs from Griffith Park in Los Angeles east through Glendale, the Eagle Rock section of Los Angeles, Pasadena, and Arcadia, ending in Monrovia. The full route was once various state highways but is now locally maintained in favor of the parallel Ventura Freeway (SR 134) and Foothill Freeway (I-210).

The west end of Colorado Boulevard is composed of two segments: a disconnected surface street segment of Colorado Boulevard, and the Colorado Street Freeway Extension. Colorado Boulevard begins at a cul-de-sac near the Los Angeles River in Los Angeles and continues east. The road passes on/off-ramps to the eastbound Colorado Street Freeway Extension, and Edenhurst Avenue, which provides access to the westbound freeway. The segment terminates at West San Fernando Road near the Los Angeles-Glendale city limits, and picks up across the railroad corridor at San Fernando Road in the city of Glendale as Colorado Street.

The Colorado Street Freeway Extension begins at Interstate 5 (Golden State Freeway) as a short freeway spur, originally carrying State Route 134 until it was moved north onto the Ventura Freeway, but is still maintained by Caltrans. After crossing the Los Angeles River, the freeway then terminates at Colorado Street in Glendale. The freeway's entrances are signed as entrances to Interstate 5. The Colorado Street Freeway Extension is part of the state highway system as Route 5S.

At the east border of Glendale, Colorado Street becomes Colorado Boulevard as it crosses State Route 2 (Glendale Freeway) into Los Angeles (specifically, the neighborhood of Eagle Rock). Another short freeway spur splits west of the intersection with Figueroa Street, heading northeast to the Ventura Freeway. This spur also carried SR 134 after the Ventura Freeway was built to the east but before it was built west of the split with the spur. After crossing Figueroa Street, Colorado Boulevard splits from Linda Vista Avenue and then passes over the Arroyo Seco on the Colorado Street Bridge into Pasadena.

In Pasadena, Colorado Boulevard crosses the short State Route 710 spur and forms the north end of State Route 110 (Arroyo Parkway). Colorado Street, renamed "Boulevard" in 1958, runs through Old Town Pasadena from Arroyo Parkway to Orange Grove Boulevard. It is the north–south zero axis of the street grid in Pasadena (the east–west axis is Fair Oaks Avenue). The Tournament of Roses parade route travels north on Orange Grove Avenue then east along Colorado Boulevard as far as Sierra Madre Boulevard, where it heads north to Victory Park. Most major Pasadena attractions are found along or within one block of Colorado Boulevard. Pasadena City College is located at 1570 East Colorado Boulevard. The street was mentioned in Jan and Dean's 1964 hit song The Little Old Lady from Pasadena. The road leaves the city into unincorporated East Pasadena, where it intersects Rosemead Boulevard (Former State Route 19), all while formerly signed as California State Route 248.

Colorado Boulevard becomes Colorado Street as it crosses Michillinda Avenue from East Pasadena into Arcadia. Through Arcadia, the street parallels the Foothill Freeway, providing access to many of the neighborhoods in west Arcadia; freeway access is provided via a separated interchange with Baldwin Avenue. Colorado Street then turns southeast and splits into two streets—Colorado Boulevard, which continues east, and Colorado Place, a short segment of old US 66 that goes southeast to merge with Huntington Drive near the Santa Anita Racetrack.

From the split, Colorado Boulevard (originally named Orange Street) becomes a primarily residential street, with some commercial zones near Santa Anita Avenue in Arcadia. The street passes under the Foothill Freeway between First and Second Streets in Arcadia with no access, in front of Monrovia High School, and through Old Town Monrovia before ending at Shamrock Avenue at Recreation Park in Monrovia. (This segment of Shamrock Avenue was once part of an early alignment of US 66 and had been named Foothill Boulevard.)

The Santa Anita Depot, built in 1890 to serve Lucky Baldwin, and the people of Rancho Santa Anita, was located at Colorado Boulevard and Old Ranch Road. It was moved to the Los Angeles County Arboretum and Botanic Garden during the construction of the 210 Foothill Freeway in 1970.