San Francisco is the fourth most populous city in California and the 12th most populous city in the United States, with a 2008 estimated population of 808,976.[8] It is the second most densely populated major city in the U.S. and is the financial, cultural, and transportation center of the larger San Francisco Bay Area, a region of more than seven million people. The city is located at the northern end of the San Francisco Peninsula, with the Pacific Ocean to the west and San Francisco Bay to the north and east, and Daly City and Brisbane to the south. Officially, it is called the City and County of San Francisco because the city constitutes the complete county, and the borders of the county match those of the city.

San Francisco is characterized by a high standard of living. The great wealth and opportunity generated by the Internet revolution continues to draw many highly educated and high-income workers and residents to San Francisco. Lower-income neighborhoods consequently have become increasingly gentrified, and many of the city's traditional business and industrial districts have experienced a renaissance driven by the redevelopment of the Embarcadero, including the neighborhoods South Beach and Mission Bay. The city's property values and household income have escalated to among the highest in the nation, allowing the city to support a large restaurant and entertainment infrastructure. Because the cost of living in San Francisco is exceptionally high, many middle class families have decided they can no longer afford to live within the city and have left.Although the centralized commerce and shopping districts of the Financial District and the area around Union Square are well-known around the world, San Francisco is also characterized by its culturally rich streetscapes featuring mixed-use neighborhoods anchored around central commercial corridors to which residents and visitors alike can walk. Because of these characteristics, San Francisco was rated "most walkable" city by the website Walkscore.com. Many neighborhoods feature a mix of businesses, restaurants and venues catering to the daily needs of the community while also drawing in visitors. Some neighborhoods are dotted with boutiques, cafes and nightlife such as Union Street in Cow Hollow, and 24th Street in Noe Valley. Others are less so, such as Irving Street in the Sunset, or Mission Street in the Mission. This approach especially has influenced the continuing South of Market neighborhood redevelopment with businesses and neighborhood services rising alongside high-rise residences.

The international character San Francisco has fostered since its founding is continued today by large numbers of immigrants from Asia and Latin America. With 39% of its residents born overseas, San Francisco has numerous neighborhoods filled with businesses and civic institutions catering to new arrivals. In particular, the arrival of many ethnic Chinese, which accelerated beginning in the 1970s, has complemented the long-established community historically based in Chinatown throughout the city and has transformed the annual Chinese New Year Parade into the largest event of its kind outside China.Following the arrival of writers and artists of the 1950s—who established the modern coffeehouse culture—and the social upheavals of the 1960s, San Francisco became an epicenter of liberal activism, with Democrats and Greens dominating city politics. Indeed, San Franciscans have not provided a Republican presidential candidate more than 20% of the vote since the 1988 election. The city's large gay population has created and sustained a politically and culturally active community over many decades, developing a powerful presence in San Francisco's civic life. A popular destination for gay tourists, the city hosts San Francisco Pride, an annual parade and festival.