Lombard Street in San Francisco, California is an east-west street that runs from The Presidio, through the Cow Hollow neighborhood (through which Lombard Street - at that point a principal arterial road - is at its busiest and widest and is co-signed as U.S. Route 101 for the 12 blocks between Broderick Street and Van Ness Avenue), and through the Russian Hill and Telegraph Hill neighborhoods, before terminating at The Embarcadero as a collector road.

Lombard Street is best known for one block on Russian Hill between Hyde and Leavenworth Streets, in which the roadway has eight sharp turns (or switchbacks) that have earned the street the distinction of being "the crookedest [most winding] street in the United States." (Vermont St. between 20th St and 22nd St near the San Francisco General Hospital may be even more crooked, but is in a much less picturesque location.) The Powell-Hyde cable car line stops at the top of this block.

The switchback design, first suggested by property owner Carl Henry and instituted in 1922, was born out of necessity in order to reduce the hill's natural 27° slope which was too steep for most vehicles to climb and a serious hazard to pedestrians used to a more reasonable sixteen-degree incline. The speed limit is a mere 5 mph (10 km/h) on the crooked section, which is about 1/4 mile (400 m) long.

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