The voice of the San Francisco Giants, Renel Brooks-Moon, is serving as Mistress of Ceremonies.
The invocation was delivered by Rabbi Beth Singer and Rev. Dr. Amos C. Brown.
Supporters in the crowd say they came here today to watch Breed make history and because they are proud of her.
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A spokesperson says there are 2,400 seats for general admission and 900 reserved seats. The seats are full and there is a crowd of supporters standing on the lawn in the Civic Center Plaza.
Breed's term will be up next November and she says she plans to run again at that time.
After today's ceremony, she is expected to greet well-wishers for a couple of hours inside her new city hall office.
For background on the San Francisco mayor's election, visit this page.