San Diego is a coastal Southern California city located in the southwestern corner of the continental United States. As of 2006, the city has an estimated population of 1,256,951. It is the second largest city in California and the eighth largest city in the United States. It is the county seat of San Diego County.GR6 and is the economic center of the San Diego–Carlsbad–San Marcos metropolitan area, the 17th-largest metro area in the U.S. with a population of 2.9 million as of 2006, and the 21st largest Metropolitan area in the Americas when including Tijuana.

San Diego County lies just north of the Mexican border—sharing a border with Tijuana—and lies south of Orange County. It is home to miles of beaches, a mild Mediterranean climate and 16 military facilities hosting the United States Navy, the United States Coast Guard and the United States Marine Corps.

The University of California, San Diego (UCSD) and the affiliated UCSD Medical Center combined with nearby research institutes in the Torrey Pines area of La Jolla make the area influential in biotechnology research. San Diego's economy is largely composed of agriculture, biotechnology/biosciences, computer sciences, electronics manufacturing, defense-related manufacturing, financial and business services, ship-repair and construction, software development, telecommunications, and tourism.

The city of San Diego it self has deep canyons separating its mesas, creating small pockets of natural parkland scattered throughout the city. The same canyons give parts of the city a highly segmented feel, creating literal gaps between otherwise proximal neighborhoods and contributing to a low-density, car-centered built environment. Downtown San Diego is located on San Diego Bay. Balboa Park lies on a mesa to the northeast. It is surrounded by several dense urban communities and abruptly ends in Hillcrest to the north. The Coronado and Point Loma peninsulas separate San Diego Bay from the ocean. Ocean Beach is on the west side of Point Loma. Mission Beach and Pacific Beach lie between the ocean and Mission Bay, a man-made aquatic park. La Jolla, an affluent community, lies north of Pacific Beach. Mount Soledad in La Jolla offers views from northern San Diego County to Mexico. Mountains rise to the east of the city, and beyond the mountains are desert areas. Cleveland National Forest is a half-hour drive from downtown San Diego. Numerous farms are found in the valleys northeast and southeast of the city. San Diego County has one of the highest count of animal and plant species that are on the endangered species list than other counties in the United States.

Communities and neighborhoods of San Diego: Old Town, San Diego. Old Town, San Diego. Northern: Bay Ho, Bay Park, Carmel Valley, Clairemont Mesa East, Clairemont Mesa West, Del Mar Mesa, La Jolla, La Jolla Village, Mission Beach, Mission Bay Park, North City, North Clairemont, Pacific Beach, Pacific Highlands Ranch, Torrey Hills, Torrey Pines, University City Northeastern: Black Mountain Ranch, Carmel Mountain Ranch, Miramar, Miramar Ranch North, Mira Mesa, Rancho Bernardo, Rancho Encantada, Rancho Peñasquitos, Sabre Springs, San Pasqual Valley, Scripps Ranch, Sorrento Valley, Torrey Highlands Eastern: Allied Gardens, Birdland, Del Cerro, Grantville, Kearny Mesa, Lake Murray, Mission Valley East, San Carlos, Serra Mesa, Tierrasanta Western: Burlingame, Hillcrest, La Playa, Linda Vista, Loma Portal, Midtown, Midway District, Mission Hills, Mission Valley West, Morena, North Park, Ocean Beach, Old Town, Point Loma Heights, Roseville-Fleetridge, Sunset Cliffs, University Heights, Wooded Area Central: Balboa Park, Bankers Hill, Barrio Logan, City Heights, Downtown (Columbia, Core, Cortez Hill, East Village, Gaslamp Quarter, Horton, Little Italy, Marina), Golden Hill, Grant Hill, Logan Heights, Memorial, Middletown, Sherman Heights, South Park, Stockton Mid-City: City Heights (comprising Azalea Park, Bayridge, Hollywood Park, Castle, Cherokee Point, Chollas Creek, Colina Del Sol, Corridor, Fairmount, Fox Canyon, Islenair, Ridgeview/Webster Rolando, Swan Canyon, Teralta East, Teralta West), College East, College West, Darnall, El Cerrito, Gateway, Kensington, Normal Heights, Oak Park, Talmadge Southeastern: Alta Vista, Bay Terrace, Broadway Heights, Chollas View, Emerald Hills, Encanto, Jamacha-Lomita, Lincoln Park, Mountain View, Mt. Hope, Paradise Hills, Shelltown, Skyline, Southcrest, Valencia Park Southern: Egger Highlands, Nestor, Ocean Crest, Otay Mesa, Otay Mesa West, Palm City, San Ysidro, Tijuana River Valley

The three largest sectors of San Diego's economy are defense, manufacturing, and tourism respectively. Several areas of San Diego (in particular La Jolla and surrounding Sorrento Valley areas) are home to offices and research facilities for numerous biotechnology companies. Major biotechnology companies like Neurocrine Biosciences and Nventa Biopharmaceuticals are headquartered in San Diego, while many biotech and pharmaceutical companies, such as BD Biosciences, Biogen Idec, Integrated DNA Technologies, Merck, Pfizer, Élan, Genzyme, Cytovance, Celgene and Vertex, have offices or research facilities in San Diego. There are also several non-profit biotech institutes, such as the Salk Institute for Biological Studies, the Scripps Research Institute and the Burnham Institute. The presence of University of California, San Diego and other research institutions helped fuel biotechnology growth. In June 2004, San Diego was ranked the top biotech cluster in the U.S. by the Milken Institute.

San Diego is home to companies that develop wireless cellular technology. Qualcomm Incorporated was founded and is headquartered in San Diego; Qualcomm is the largest private-sector technology employer (excluding hospitals) in San Diego County.[14] The largest software company in San Diego (acccording to the San Diego Business Journal) is security software company Websense Inc. Websense was founded and is headquartered in San Diego.

The economy of San Diego is influenced by its port, which includes the only major submarine and shipbuilding yards on the West Coast, as well as the largest naval fleet in the world. The cruise ship industry, which is the second largest in California, generates an estimated $2 million annually from the purchase of food, fuel, supplies, and maintenance services.[15] Due to San Diego's military influence, major national defense contractors, such as General Atomics and Science Applications International Corporation are headquartered in San Diego. Tourism is also a major industry owing to the city's climate. Major tourist destinations include Balboa Park, the San Diego Zoo, Seaworld, nearby Wild Animal Park and Legoland, the city's beaches and golf tournaments like the Buick Invitational.

San Diego has several sports venues: Qualcomm Stadium is the home of the NFL San Diego Chargers, NCAA Division I San Diego State Aztecs, as well as local high school football championships. Qualcomm Stadium also hosts international soccer games, Supercross events and formerly hosted Major League Baseball. Three NFL Super Bowl championships and many college football bowl games have been held there. Balboa Stadium is the city's first stadium, constructed in 1914, and former home of the San Diego Chargers. Currently Balboa Stadium hosts soccer, American football and track and field.

PETCO Park in downtown San Diego is the home of Major League Baseball's San Diego Padres. The ballpark is also the current home of the semi-final and final games of the World Baseball Classic series, having hosted the inaugural series championship games in 2006. PETCO Park will be the home to the 2009 World Baseball Classic semi-finals and final as well. Other than baseball, PETCO Park hosts other occasional soccer and rugby events. The San Diego Sports Arena hosts basketball, and has also hosted ice hockey, indoor soccer and boxing. Cox Arena at Aztec Bowl on the campus of San Diego State University hosts the NCAA Division I San Diego State Aztecs men's and women's basketball games. Torero Stadium at the University of San Diego hosts college football and soccer, and the Jenny Craig Pavilion at USD hosts basketball and volleyball.

The San Diego State Aztecs (MWC) and the San Diego Toreros (WCC) are NCAA Division I teams. The UCSD Tritons (CCAA) are members of NCAA Division II while the Point Loma Nazarene Sea Lions (GSAC) are members of the NAIA. San Diego has been the home of two NBA franchises, the first of which was called the San Diego Rockets. The Rockets represented the city of San Diego from 1967 until 1971. After the conclusion of the 1970-1971 season, they moved to Texas where they became the Houston Rockets. Seven years later, San Diego received a relocated NBA franchise (the Buffalo Braves), which was renamed the San Diego Clippers. The Clippers played in the San Diego Sports Arena from 1978 until 1984. Prior to the start of the 1984-1985 season, the team was moved to Los Angeles, and is now called the Los Angeles Clippers. Other sports franchises that represented San Diego include the San Diego Conquistadors of the American Basketball Association, the San Diego Sockers (which played in various indoor and outdoor soccer leagues during their existence), the San Diego Flash and the San Diego Gauchos, both playing in different divisions of the United Soccer League, the San Diego Spirit of the Women's United Soccer Association, the San Diego Mariners of the World Hockey Association, and the San Diego Gulls who were in different hockey leagues during each of their three incarnations. The San Diego Riptide and the San Diego Shockwave were indoor football teams that played at the Sports Arena and Cox Arena, respectively. San Diego has long been a candidate for a Major League Soccer franchise, especially due to the city recording FIFA World Cup television audiences which are double the national average. Curiously, despite positive language being expressed by the league, the city, the media and the public, a franchise continues to elude San Diego. That looks likely to be finally rectified with San Diego considered among the favourites to land one of three franchises to be offered before 2010. The city does currently have an active mens team playing in the fourth level of American soccer, the San Diego Pumitas but no approaches have been made to turn them into an MLS team as yet.

According to education rankings released by the U.S. Census Bureau, 40.4 percent of San Diegans ages 25 and older hold bachelor's degrees. The census ranks the city as the ninth most educated city in the United States based on these figures. Public colleges and universities in the city include University of California, San Diego (UCSD), San Diego State University (SDSU), and the San Diego Community College District, which includes San Diego City College, San Diego Mesa College, and San Diego Miramar College. Private colleges and universities in the city include Alliant International University (AIU), Design Institute of San Diego (DISD), John Paul the Great Catholic University, National University, NewSchool of Architecture and Design, Pacific Oaks College, The Art Institute of California, San Diego, Point Loma Nazarene University (PLNU),Woodbury University School of Architecture's satellite campus, and University of San Diego (USD) . There is one medical school in the city, the UCSD School of Medicine. There are three ABA accredited law schools in the city, which include California Western School of Law, Thomas Jefferson School of Law, and University of San Diego School of Law. There is also one unaccredited law school, Western Sierra Law School. The Joint Mathematics Meeting of the MAA, that is, Mathematical Association of America and AMS, which denotes American Mathematical Society, took place in San Diego, January, 2008.

The San Diego Unified School District, also known as San Diego City Schools, is the school district that serves the majority of the city, it includes 113 elementary schools, 23 middle schools, 4 atypical schools, 10 alternative schools, 27 high schools and 25 charter schools. In the northern part of the county, Poway Unified School District and San Dieguito Union High School District are districts outside city limits, but serve several schools within city limits. In the southern part of the county, Sweetwater Union High School District serves multiple schools within city limits, although it is headquartered outside city limits. San Ysidro School District (K-8) serves areas of San Diego also served by Sweet Water Union High School District. Del Mar Union Elementary School District and Solana Beach Elementary School District serve areas of San Diego also within San Dieguito.