Los Angeles is the second largest city in the United States, and with a population of 3.8 million is the largest city in the state of California and the Western United States. Additionally the city spans over 498.3 square miles (1,290.6 km2) in Southern California and is anchored to the world's 13th largest metropolitan area with 17.7 million people spread out over much of coastal Southern California. The Los Angeles–Long Beach–Santa Ana metropolitan area is home to nearly 12.9 million residents. Los Angeles is also the seat of Los Angeles County, the most populated and one of the most multicultural counties in the United States. The city's inhabitants are referred to as "Angelenos".

Los Angeles was founded on September 4, 1781, by Spanish governor Felipe de Neve as El Pueblo de Nuestra Señora la Reina de los Angeles del Río de Porciúncula (The Village of Our Lady, the Queen of the Angels of the river of Porziuncola). It became a part of Mexico in 1821, following its independence from Spain. In 1848, at the end of the Mexican-American War, Los Angeles and the rest of California were purchased as part of the Treaty of Guadalupe Hidalgo, thereby becoming part of the United States; Mexico retained the territory of Baja California. Los Angeles was incorporated as a municipality on April 4, 1850, five months before California achieved statehood.

Often known by its initials, L.A., and nicknamed The City of Angels, Los Angeles is a world center of business, international trade, entertainment, culture, media, fashion, science, technology, and education. It is home to renowned institutions covering a broad range of professional and cultural fields, and is one of the most substantial economic engines within the United States. In 2008, Los Angeles was named the world's eighth most economically powerful city by Forbes.com, ahead of Shanghai and Toronto but behind New York City and London. As the home base of Hollywood, it is known as the "Entertainment Capital of the World", leading the world in the creation of motion pictures, television production, video games, and recorded music. The importance of the entertainment business to the city has led many celebrities to call Los Angeles and its surrounding suburbs home.

The economy of Los Angeles is driven by international trade, entertainment (television, motion pictures, video games, recorded music), aerospace, technology, petroleum, fashion, apparel, and tourism. Los Angeles is also the largest manufacturing center in the western United States. The contiguous ports of Los Angeles and Long Beach together comprise the fifth busiest port in the world and the most significant port in the Western Hemisphere and is vital to trade within the Pacific Rim. Other significant industries include media production, finance, telecommunications, law, healthcare, and transportation. The Los Angeles-Long Beach-Riverside combined statistical area (CSA) has a gross metropolitan product (GMP) of $831 billion (as of 2008), making it the third largest economic center in the world, after the Greater Tokyo Area and the New York-Newark-Bridgeport CSA. If counted as a country, the surrounding CSA has the 15th largest economy in the world in terms of nominal GDP, placing it just below Australia and above the Netherlands, Turkey, Sweden, Belgium, and Indonesia.

Until the mid-1990s, Los Angeles was home to many major financial institutions in the western United States. Mergers meant reporting to headquarters in other cities. For instance, First Interstate Bancorp merged with Wells Fargo in 1996, Great Western Bank merged with Washington Mutual in 1998, and Security Pacific Bank merged with Bank of America in 1992. Los Angeles was also home to the Pacific Exchange, until it closed in 2001.

The city is home to six Fortune 500 companies. They are aerospace contractor Northrop Grumman, energy company Occidental Petroleum, healthcare provider Health Net, metals distributor Reliance Steel & Aluminum, engineering firm AECOM, and real estate group CB Richard Ellis.

Other companies headquartered in Los Angeles include City National Bank, 20th Century Fox, Latham & Watkins, Univision, Metro Interactive, LLC, Premier America, Gibson, Dunn & Crutcher, DeviantArt, Guess?, O’Melveny & Myers; Paul, Hastings, Janofsky & Walker, Tokyopop, The Jim Henson Company, Paramount Pictures, Sunkist Growers, Incorporated, Tutor Perini, Fox Sports Net, Capital Group, 21st Century Insurance, and The Coffee Bean & Tea Leaf. Korean Air's US passenger and cargo operations headquarters are located in two separate offices in Los Angeles.

The metropolitan area contains the headquarters of companies who moved outside of the city to escape its taxes but keep the benefits of proximity. For example, Los Angeles charges a gross receipts tax based on a percentage of business revenue, while many neighboring cities charge only small flat fees. The companies below benefit from their proximity to Los Angeles, while at the same time avoiding the city's taxes (and other problems).

Some of the major companies headquartered in the cities of Los Angeles county are Shakey's Pizza (Alhambra), Academy of Motion Picture Arts and Sciences (Beverly Hills), Hilton Hotels (Beverly Hills), DIC Entertainment (Burbank), The Walt Disney Company (Fortune 500 – Burbank), Warner Bros. (Burbank), Countrywide Financial (Fortune 500 – Calabasas), THQ (Calabasas), Belkin (Compton), Sony Pictures Entertainment (parent of Columbia Pictures, located in Culver City), DirecTV (El Segundo), Mattel (Fortune 500 – El Segundo), Unocal Corporation (Fortune 500 – El Segundo), DreamWorks (Glendale), Sea Launch (Long Beach), ICANN (Marina del Rey), Cunard Line (Santa Clarita), Princess Cruises (Santa Clarita), Activision (Santa Monica), and RAND (Santa Monica).

The University of Southern California (USC) is the city's largest private sector employer and contributes $4 billion annually to the local economy. Los Angeles is classified as a "beta+ world city" in a 2008 study by a research group at Loughborough University in England.

In January 2010 many of the aerospace firms with operations in Los Angeles County are relatively small compared to the larger corporations.