San Diego (pronounced /ˌsændiˈeɪgoʊ/) 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. and is the economic center of the 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 (See San Diego-Tijuana Metro.).

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.