More than half of the land area of the city of Los Angeles lies within the San Fernando Valley. The other incorporated cities in the valley are Burbank, Glendale, San Fernando, Hidden Hills and Calabasas.

The San Fernando Valley is about 260 square miles (670 km2) bounded by the Santa Susana Mountains to the northwest, the Simi Hills to the west, the Santa Monica Mountains and Chalk Hills to the south, the Verdugo Mountains to the east, and the San Gabriel Mountains to the northeast. The northern Sierra Pelona Mountains, northwestern Topatopa Mountains, southern Santa Ana Mountains, and Downtown Los Angeles skyscrapers, can be seen from higher neighborhoods, passes, and parks in the San Fernando Valley.

The Los Angeles River begins at the confluence of Calabasas Creek (Arroyo Calabasas) and Bell Creek (Escorpión Creek) at Canoga Park High School beside Vanowen Boulevard in Canoga Park. Those creeks' headwaters are in: the Santa Monica's Calabasas foothils; and the Simi Hill's Hidden Hills, Santa Susana Field Laboratory, and Santa Susana Pass Park lands. The River flows eastward along the southern regions of the Valley. One of the river's two unpaved sections can be found at the Sepulveda Basin. The seasonal river, the Tujunga Wash, drains much of the western facing San Gabriel Mountains, and passes through the Hansen Dam Recreation Center in Tujunga south along the Verdugo Mountains through the eastern communities of the Valley to join the Los Angeles River in Studio City. Other notable tributaries of the River include Dayton Creek, Caballero Creek, Bull Creek, Pacoima Wash, and Verdugo Wash. The elevation of the floor of the valley varies from about 600 to 1,200 ft. above sea level.

Most of the San Fernando Valley is within the jurisdictional boundaries of the city of Los Angeles, although a few other incorporated cities are located within the Valley as well; Burbank and Glendale are in the southeast corner of the Valley, Hidden Hills, Calabasas, and Bell Canyon are in the southwest corner, and San Fernando, which is completely surrounded by Los Angeles, is in the northeast valley. Universal City, an enclave in the southern part of the Valley, is unincorporated land housing the Universal Studios filming lot. Mulholland Drive, which runs along the ridgeline of the Santa Monica Mountains, marks the boundary between the Valley and the communities of Hollywood and the Los Angeles Westside.

San Fernando Valley is composed of six incorporated cities. The majority of the valley is governed by the incorporated City of Los Angeles. The unincorporated communities (Census-designated places) are governed by County of Los Angeles.

The Los Angeles city section of the valley is divided into seven city council districts. They are City Council districts 2, 3, 4, 5, 6, 7 and 12. Of the 99 neighborhood councils in the city, 34 are in the Valley. The valley is represented in the California State Legislature by seven members of the State Assembly and five members of the State Senate. The valley is divided into five congressional districts. It is represented in Congress by senior figures from both parties including Representative Henry Waxman (D), Representative Howard Berman (D), and Representative Howard McKeon (R). In the Los Angeles County Board of Supervisors, it is represented by two supervisorial districts.

The San Fernando Valley votes largely for Democratic candidates in local, state, and national elections. However, along with the Los Angeles Harbor district, it also elects Republican candidates.

The Los Angeles satellite administrative center for the valley, The Civic Center Van Nuys, is in Van Nuys. The area in and around the Van Nuys branch of Los Angeles City Hall is home to a police station, municipal and superior courts and Los Angeles city and county administrative offices. Northridge is home to California State University Northridge (originally named San Fernando Valley State College).

The Tongva, later known as the Fernandeño=Gabrieleño Mission Indians after colonization, and the Tataviam to the north and Chumash to the west, had lived and thrived in the Valley and its arroyos for over 8,000 years. They had numerous settlements, and trading and hunting camps, before the Spanish arrived and took their homeland in 1797 for the Mission San Fernando Rey de España and Las Californias ranchos.

The first Spanish land grant in the San Fernando Valley or El Valle de Santa Catalina de Bononia de los Encinos, called 'Rancho Encino' (present day Mission Hills on the Camino Viejo before Newhall Pass), in the northern part of the San Fernando Valley. Juan Francisco Reyes built an adobe dwelling was built beside a Tongva village or rancheria at natural springs, but 'Rancho Encino' was short lived with the land traded so a Mission could be sited and built there. Mission San Fernando Rey de España was established in 1797 as the 17th of the twenty-one missions. The land trade granted Juan Francisco Reyes the similarly named Rancho Los Encinos, also beside springs (Los Encinos State Historic Park in present day Encino). Later the Mexican land grants of Rancho El Escorpión (West Hills), Rancho Providencia and Rancho Cahuenga (Burbank), and Rancho Ex-Mission San Fernando (rest of valley) were established to cover the San Fernando Valley.