State Route 90 (SR 90) is a state highway in Southern California, United States. It consists of two unconnected pieces in Greater Los Angeles.

The Marina Freeway segment is a short freeway in southwestern Los Angeles and the nearby suburbs, linking Marina del Rey to the rest of Greater Los Angeles. The limited-access portion runs from Slauson Avenue in southern Culver City to just past Culver Boulevard, where it forms the approximate border between the Del Rey and Westchester neighborhoods of the city of Los Angeles. The route continues westward into unincorporated Marina del Rey as an expressway, terminating at Lincoln Boulevard.

The eastern portion of Route 90 is Imperial Highway connecting La Habra, Brea, Yorba Linda and Anaheim Hills. The part in Yorba Linda was relinquished in 2002, and the portion built to freeway standards is now known by two names: The Richard M. Nixon Parkway between Yorba Linda Blvd. and Kellogg Drive, and the Richard M. Nixon Freeway between Kellogg Drive and its southern terminus at Orangethorpe Avenue.

This route is part of the California Freeway and Expressway System.

The west segment of SR 90 begins at Lincoln Boulevard (State Route 1) in the Del Rey district of Los Angeles. It heads east along the Marina Expressway, past several intersections, and becomes the Marina Freeway after crossing Ballona Creek. After two interchanges - with Centinela Avenue and Interstate 405 - SR 90 and the freeway end at Slauson Avenue.

The east segment begins at the intersection of Imperial Highway and Beach Boulevard (State Route 39) in La Habra. It heads east and southeast on Imperial Highway, ending at State Route 91 about 1/4 mile (400 m) after crossing the Santa Ana River from Yorba Linda into Anaheim. A portion of the road in Yorba Linda is built to freeway standards; it is now known as the Richard M. Nixon Parkway after the city accepted maintenance in 2002. However, the same state law that authorized relinquishment required the city to "maintain signs directing motorists to the continuation of Route 90".

There were once plans to connect the two sections via the Slauson Freeway and Yorba Linda Freeway, mostly parallel to Slauson Avenue, but this was never built. The full route was added to the California Freeway and Expressway System in 1959.

Legislative Route 221 (the Slauson Freeway, now the Marina Freeway) was defined in 1947 to run from pre-1964 Legislative Route 60 (now State Route 1) east to pre-1964 Legislative Route 165 (now Interstate 110). A 1959 extension took it east to pre-1964 Legislative Route 170 (now Interstate 605).

To the east, Legislative Route 176 (the Yorba Linda Freeway, now also the Marina Freeway) was defined in 1939 from pre-1964 Legislative Route 62 (now State Route 39) east and southeast to pre-1964 Legislative Route 43 (now State Route 91). A 1959 extension took it west to pre-1964 Legislative Route 174 (later State Route 42) near Norwalk.

In the 1964 renumbering, LR 221 was assigned State Route 90, but LR 176 all became part of State Route 42, along with the connecting LR 174 to the west. The piece of LR 176 between I-605 and SR 39 was reassigned to SR 90 in 1965, and the rest east to SR 91 became part of SR 90 in 1968 (at the same time as SR 42 became Interstate 105).

Originally planned as the Slauson Freeway, Route 90 was slated to extend across southern Los Angeles County and northern Orange County, ending at the Riverside Freeway in eastern Anaheim. However, by the 1960s, community opposition had reduced it to what is effectively a minor spur of I-405 to Marina Del Rey (derisively dubbed the "Slauson Cutoff" by comedian Johnny Carson). It was renamed the Richard M. Nixon Freeway for a brief period in the early 1970s, but after Nixon's resignation in the wake of the Watergate scandal, its name was changed to the current appellation.

From I-405 west to Centinela Avenue, the Marina Freeway is 8 lanes wide, before it quickly narrows to 4 lanes at the Culver Boulevard exit. The freeway ends approximately 1/2 mile west of Culver Boulevard, and continues as an expressway. There has been talk of extending the Marina Expressway slightly west of Lincoln Boulevard (Route 1) to Admiralty Way (approximately 1/4 mile) to accommodate ongoing expansion of the Marina Del Rey area. Strong opposition to this makes actualization of this plan uncertain.

In 2002 the City of Yorba Linda assumed responsibility for Imperial Highway within its city limits due to AB 887; it lost its state route designation,[citation needed] and is now called the Richard M. Nixon Parkway.

By 2005, construction on the western end of the Marina Freeway began, to extend the freeway terminus from Culver Boulevard to approximately 1/2 mile west of Culver Boulevard by building a full interchange at Culver. The freeway extension was completed in early 2007. The freeway extension also allows Route 90 drivers to avoid a traffic signal at Alla Road (just west of Culver Boulevard.). After the end of the freeway, a pair of frontage roads operating as an expressway continues as Route 90 up to Route 1 (Lincoln Boulevard). Signalized intersections occur at Mindanao Way and Lincoln Boulevard, which is the end of the expressway in Marina del Rey. The reason for the extension is to relieve traffic congestion on surface streets.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.