The San Fernando Valley is 345 square miles (894 km²) bounded by the Santa Susana Mountains to the northwest, the Simi Hills to the west, the Santa Monica Mountains to the south, the Verdugo Mountains to the east, and the San Gabriel Mountains to the northeast. The Sierra Pelona Mountains (to the north) can be seen in parts of the San Fernando Valley from the gap between the Santa Susana and San Gabriel (Newhall Pass). The Los Angeles River starts at the confluence of Calabasas and Bell Canyon creeks behind Canoga Park High School in Canoga Park and flows east along the southern areas of the Valley. One of the river's only unpaved section can be found at the Sepulveda Basin. Another waterway, the Tujunga Wash, drains much of the western San Gabriel Mountains and, after passing through the Hansen Dam Recreation Center, winds south through the eastern communities of the Valley before merging with the Los Angeles River in Studio City. Other tributaries of the Los Angeles River include Caballero Creek, Bull Creek, Pacoima Wash, and Verdugo Wash. The valley's elevation varies from between about 250 and 1,200 ft. above sea level.

Most of the San Fernando Valley is within the City of Los Angeles, California, although several smaller cities are within the Valley as well; Burbank and Glendale are in the southeast corner of the Valley, Hidden Hills and Calabasas are in the southwest corner, and San Fernando, which is completely surrounded by the City of 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 Los Angeles' westside.

Los Angeles' administrative center for the Valley is in Van Nuys. The area in and around the former Van Nuys 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. The 1994 Northridge Earthquake (January 17, 1994 which measured 6.7 on the Richter Scale), one of the few major earthquakes to have struck directly under a major city, was epicentered in neighboring Reseda just east of the intersection of Elkwood Street and Baird Avenue. An earlier major temblor (in 1971), The Sylmar Quake (February 9, 1971 and measured 6.5 on the Richter Scale), was also a killer, having destroyed the Olive View and Veterans Administration Hospitals, and rendered the east west Interstate 210 useless for a number of years due to severe damage. Prior to development, before the arrival of the Los Angeles Owens Valley Aqueduct water, the valley was a bleak semi-desert, too dry for extensive agriculture over more than a small part of the valley. The water brought farming with some major crops including corn, cotton, persimmons, lemons, oranges, and walnuts. The advent of three new industries - motion picture, automobile, and aircraft - spurred urbanization and population growth. World War II and a subsequent post war boom accelerated this growth so that by 1960, the valley had a population of well over 1 million.

The Valley shares the Los Angeles Basin's dry, sunny weather. Although the southwestern edge of the Valley is less than 10 miles from the Pacific Ocean, the Valley can be considerably hotter than the Los Angeles Basin during the summer months and cooler during the winter months. The West Valley community of Woodland Hills has set the highest recorded temperature in the City of Los Angeles of 119 °F (49 °C) in 2006, the coldest recorded temperature was in Canoga Park 18 °F (-8 °C) in 1989. Also, rainfall accumulations tend to be slightly higher in the Valley during the rainy season in comparison to the Los Angeles Basin and the coast. The valley is more likely to get snow during winter months than the Los Angeles basin, although snow in San Fernando valley is quite rare. The last measurable accumulation of snow in the valley was in 1988 while the last measurable accumulation of snow in the Los Angeles basin was in 1960. The Valley is prone to smog, particularly in the summer, because of the mountain ranges surrounding it and because vertical motion in the atmosphere is often blocked by temperature inversions. Environmental regulations and improvements through the years have cut the smog levels almost in half since they peaked in the 1960s.

The Tataviam, also known as the Fernandeño, tribe of Indians and the Tongva had inhabited the valley for almost 2,000 years before the Spanish built the San Fernando Mission in 1797.

The treaty ending the Mexican-American War in California was signed near the mouth of the Cahuenga Pass (at the southeast corner of San Fernando Valley) at the Campo de Cahuenga in 1847.

After the construction of the Owens Valley-Los Angeles Aqueduct, the mostly rural area was annexed by the city of Los Angeles in 1915, more than doubling the size of the city. A highly fictionalized story based on these events is told in the film Chinatown (1973). Los Angeles continued to consolidate its territories in the San Fernando Valley by annexing Laurel Canyon (1923), Lankershim (1923), Sunland (1926), Tuna Canyon (1926), the incorporated city of Tujunga (1932), and Porter Ranch (1965). The additions expanded the Los Angeles portion of San Fernando Valley from the original 169 square miles (438 km²) to 224 square miles (580 km²) today. Six cities incorporated independent from Los Angeles: Glendale (1906), Burbank (1911), San Fernando (1911) Hidden Hills (1961), Calabasas (1991). Universal City is an unincorporated enclave that is home to Universal Studios theme park and Universal CityWalk.

In 2002, Los Angeles residents defeated a proposal under which the San Fernando Valley portion of the City of Los Angeles would have seceded and become an independent incorporated city of its own. Had the proposal passed, it would have created a new municipality of 211 square miles (546 km²) with about 1.3 million residents. The new Valley City would have been the sixth most populous city in the U.S., just ahead of Phoenix. Los Angeles would have become the third largest city in the nation, behind New York City and Chicago.

The Valley attempted to secede in the 1970s, but the state passed a law barring city formation without the approval of the City Council. In 1997, Assemblymen Bob Hertzberg and Tom McClintock helped pass a bill that would make it easier for the Valley to secede by removing the City Council veto. AB 62 was signed into law by Governor Pete Wilson. Meanwhile, a grassroots movement to split the Los Angeles Unified School District (LAUSD) and create new San Fernando Valley-based school districts became the focal point of the desire to leave the city. Though the state rejected the idea of Valley-based districts, it remained an important rallying point for Hertzberg's mayoral campaign, which proved unsuccessful.

Before secession could come out for a vote, the Local Agency Formation Commission (LAFCO) studied the fiscal viability of the new city and decided that the new city must mitigate any fiscal loss incurred by the rest of Los Angeles. LAFCO concluded that a new San Fernando Valley city would be financially viable, but would need to mitigate the $60.8 million that Los Angeles would lose in revenues. Secessionists took this figure as evidence that the Valley gave more money to Los Angeles than it received back in services. This triggered a petition drive led by Valley VOTE to put secession on the ballot. Measures F and H not only decided whether the Valley became a city but voters also got to pick a new name for it. The proposed names on the ballot were as follows: San Fernando Valley, Rancho San Fernando, Mission Valley, Valley City and Camelot. Along with Measures F and H, elections were held for fourteen council members and a mayor.

Valley politicians such as State Senator Richard Alarcon and City Council President Alex Padilla opposed the initiatives. The leader of the LAUSD breakup and former congresswoman and busing opponent Bobbie Fiedler also campaigned against secession. Supporters pointed out that the Valley suffered from many of the same problems of poverty, crime, drug and gang activity as the rest of the city.

The proposal passed with a slight majority in the Valley, but was defeated by the rest of Los Angeles voters due to a heavily-funded campaign against it led by Los Angeles mayor James Hahn. Republican Assemblyman Keith Richman of Northridge was voted in as mayor of the stillborn city. Richman and other activists behind the secession movement attempted to redirect their civic energies toward influencing Los Angeles city politics, but their efforts largely fizzled. Hertzberg's 2005 mayoral campaign, which received heavy support in the Valley, nonetheless finished in third place (only a few percentage points behind incumbent Mayor Hahn), and no secession supporters were elected to positions on the Los Angeles City Council.

Many neighborhoods of Los Angeles in the San Fernando Valley have 'seceded' from one another in the form of renaming and reforming known community boundaries. Groups are motivated by the desire to disassociate themselves from undesirable connotations that some communities have inherited and, in the process, increase property values. Lake Balboa broke away from Van Nuys. Valley Village, Studio City and Valley Glen separated from North Hollywood. West Hills and Winnetka separated from Canoga Park. Porter Ranch seceded from Northridge. Arleta successfully broke off from Pacoima but was thwarted in its attempts to carve out a separate ZIP code. The separate districts are in name only as none of the communities have actual governmental authority and all of the communities remain politically a part of the City of Los Angeles.

The San Fernando Valley had a population 1,696,347 in 2000. A recent estimate by the Los Angeles County Urban Research Unit and Population Division puts the 2004 population at 1,808,599. The largest cities entirely in the valley are Glendale and Burbank. The largest sections of Los Angeles in the valley are North Hollywood and Van Nuys. Each of the two districts and each of the two sections of Los Angeles mentioned has more than 100,000 residents. Despite the San Fernando Valley's reputation for sprawling, low-density development, the Valley communities of Panorama City, North Hollywood, Van Nuys, Reseda, Canoga Park, and Northridge, all in Los Angeles, have numerous apartment complexes and contain some of the densest census tracts in Los Angeles.

Latinos and non-Hispanic whites are nearly even in numbers, combining to comprise more than four out of five Valley residents. In general, communities in the northeastern, central, and southeastern parts of the Valley have the highest concentration of Latinos. Non-Hispanic Whites live mainly along the communities along the region's mountain rim and in the northwestern and southern sections of the valley. The city of Glendale has an influential and very large Armenian community. The cities of San Fernando, Calabasas, Hidden Hills, and the Tarzana area of Los Angeles are quite homogeneous in racial makeup.

Asian Americans make up 10.7% of the population and live throughout the Valley, but are most numerous in the city of Glendale and the Los Angeles communities of Chatsworth, Panorama City, Porter Ranch and Granada Hills. African Americans compose 5.1% of the Valley's population, living mainly in the Los Angeles sections of Lake View Terrace, Pacoima, Reseda, Valley Village, Van Nuys, and Northridge. Another large ethnic element is the Iranian community with 200,000 people living mainly in west San Fernando Valley. The valley is also home to a large and influential Jewish community.

Poverty rates in the San Fernando Valley are lower than the rest of the county (15.3% compared to 17.9%). Eight San Fernando Valley communities have at least one in five residents living in poverty.

The Pacoima section of Los Angeles is widely known in the region as a hub of suburban blight. Other San Fernando Valley communities, such as the Los Angeles sections of Mission Hills, Arleta, and Sylmar, have poverty rates well below the regional average, even lower than neighborhoods populated by a higher number of Non-Hispanic White residents. Leonardo Di Caprio is native to Pacoima.

Many wealthy families live in the hills south of Ventura Boulevard; as a result, the phrase "South of the Boulevard" has become a commonly used buzzword in local real estate.  Without Further Adue, WE LOVE YOU Yvette Tolliver