San Francisco International Airport (SFO) is the primary airport serving San Francisco. 
Click here for the SFO website. 

An alternative is San Jose International Airport (SJC).  Transportation options are
given on the SJC website.

Transportation from SFO

       Bay Area Rapid Transit (BART):   Cost:  $4.95
       BART is the public transit train system for San Francisco.  The station is located in the
         airport and can be reached by taking the Air Train to the BART connection.
        Take BART to the Powell Street Station, located approximately 3 blocks
         from the St. Francis Hotel (conference location).  Refer to map below for exact  
         location.  Click here to access the BART website.

        Airport Shuttles
       A number of shuttles are available from SFO to downtown San Francisco hotels.
         As an example, Supershuttle charges $13.50 one-way.
  
      Taxis
      One-way taxi fare from SFO to the St. Francis is approximately $40. 

      Rental Cars
      Rental cars are available at the airport and can be reached by taking the Air Train.
        However, public transportation within San Francisco is very good and a car is not
        necessary.  Parking is also expensive.  For excursions outside the city, cars can be
        rented from the hotel.