Here is a list of the major airports in California.  Please note: there are other, smaller airports in the state but the first 10 on this list are the most well-known and have the majority of commercial flights.

The San Francisco Bay Area has three airports:

(The first two are the more common portals for those visiting the city of San Francisco and adjacent area)

SFO (San Francisco International -- one of two airports, along with LAX, responsible for most international travel).

OAK (Oakland International Airport) often a less expensive option than SFO and is the closest Bay Area Airport to Napa.

The above 2 airports are linked by BART, the local public transit system.    

SJC (Mineta San Jose International Airport).  The airport is located in the city of San Jose.  To get to San Francisco, one can take the Bus Shuttle to Caltrain the commuter train which services the San Jose to San Francisco corridor .  It is the closest airport to Silicon Valley, San Jose, and the new Levi's Stadium in Santa Clara, home to the San Francisco 49'ers.

In Sacramento, there is one major airport: 

SMF (Sacramento) The State Capitol. 11 airlines serving the USA and Mexico. 

In the Greater Los Angeles area (aka the Southland), there are five major airports: 

LAX (Los Angeles International), the main International portal in California with major domestic travel as well. (One of the busiest airports in the world). The airport is located in the southwest corner of the city of Los Angeles.

BUR (Bob Hope Airport aka Burbank Airport), a small (two terminals), domestic-traffic-only airport in the city of Burbank, just north of the Los Angeles neighborhood of Hollywood.  The airport is, therefore, located just outside of the northeast corner of the city of Los Angeles. has discount flights into BUR from many cities in the U.S. including Las Vegas, San Francisco and Oakland (adjacent to San Francisco).

LGB (Long Beach Airport), a small (one terminal), domestic-traffic-only airport in the southeast corner of the county of Los Angeles, to the south of downtown Los Angeles. has discount flights into LGB from a number of cities in the U.S. including New York, Boston and Las Vegas.

SNA (John Wayne Airport aka Orange County aka Santa Ana Airport), largely, a domestic-traffic airport but with limited service to select cities in Mexico and Canada.  The airport is located in Orange County, which is southeast of both the city of Los Angeles and the county in which it is located.

ONT  (LA/Ontario International Airport aka Ontario Airport), largely, a domestic-traffic airport but with very limited international service to 2 or 3 cities in Mexico.  The airport is located in San Bernardino County in the city of Ontario which is east of the city of Los Angeles.

In San Diego, there is one major airport: 

SAN  (San Diego Airport)  Lindbergh Field. Domestic and International, 23 airlines  

Additionally, there are several smaller airports which serve popular tourist locations:

STS (Sonoma County Airport), Charles M. Schultz serves the Santa Rosa/Healdsburg/Sonoma County area.

PSP (Palm Springs International Airport), serves the Desert Area of Southern California, Palm Springs, Palm Desert, Rancho Mirage and Indio.

SBA (Santa Barbara Municipal Airport), serves the popular tourist destination of Santa Barbara and is the main airport for the Central Coast.

FAT (Fresno Yosemite International Airport), Central California’s main airport is also the closest airport to Yosemite National Park.

ACV  (Arcata/Eureka) located in Arcata is the closest airport to Redwood National Park.

Also worth noting...

Although not in California, LAS (McCarran International Las Vegas Airport) and RNO (Reno-Tahoe International Airport) are also popular gateway airports to California. RNO for example is the closet airport for Lake Tahoe and the California ski resorts there.

Some airlines in the USA are "discount" airlines who sell most or all of their tickets through their own websites instead of through a travel agent or major travel website. (The airport links above will list the specific airlines serving each airport and how to reach them). Examples of airlines like these include: Southwest  Frontier  JetBlue  Virgin America and Spirit Air

Transferring between Los Angeles and San Diego is best accomplished by car or rail since the cities are only approximately 2 hours, 15 minutes apart.  When traveling between Los Angeles and the San Francisco Bay Area, air travel can be more cost effective. While the train trip from Los Angeles to the Bay Area can be scenic, it is time consuming. Driving is also a popular option and, often, the quickest and most direct, means of transport.

For rail travel options in California, visit this page, California Rail Travel.

For Long Distance express bus service serving California, check MegaBus and BoltBus.