By ship
Golden Gate Ferry
Service to and from Larkspur and Sausalito.
Blue & Gold Fleet
Offering services between the Ferry Building and Angel Island, Oakland/Alameda, Tiburon and Vallejo.
BayLink Ferry
Service to and from Vallejo.
Alameda Oakland Ferry
Service to and from Alameda and Oakland.
Harbor Bay Ferry
Service to and from Bay Farm Island in Alameda.
By Public Transit
Extensive public transit is offered through the neighborhood, provided either by the regional BART (http://www.bart.gov/index.asp) system or the city-wide MUNI (http://www.sfmta.com/cms/...) system, which encompasses the MUNI Metro, buses, cable cars, and the F-Line streetcar.
BART and all of the MUNI Metro lines J, K, L, M, N and T run under Market Street with three stations serving this part of downtown: the Embarcadero, Montgomery Street and Powell Street. The Powell Street stop is just a few blocks down Powell from Union Square. The Powell-Hyde and Powell-Mason cable car lines run from Powell and Market past Union Square to Fisherman's Wharf. From the Embarcadero station you can catch the California cable car line.
The F Streetcar Line runs along Market Street and up the Embarcadero to Fisherman's Wharf. There are several streetcar stops along Market Street. Numerous MUNI bus lines run through the area as well, such as the 38-Geary which runs past Union Square and the 1-California which runs through the Financial District past the Embarcadero Center. The #10, #30 and #45 lines run north-south through the district, connecting to Chinatown, North Beach, and Fisherman's Wharf to the north.
By car
On-street parking is all but non-existent. Parking garages, while plentiful, can be expensive. Major parking garages for the Union Square area can be found at the NE corner of Sutter and Stockton, between Ellis and O'Farrell between Stockton and Powell, on Sutter between Kearny and Grant, and under Union Square.