On December 1, 1955, Rosa Parks refused to give up her seat to a white passenger on a bus in Montgomery, Alabama. Her arrest sparked a boycott of the city's bus system.
See Today's Document from the U.S. National Archives:
Illustration of bus where Rosa Parks sat, December 1, 1955
Diagram of the Bus Showing Where Rosa Parks Was Seated (ARC Identifier: 596069); File Unit: Aurelia S. Browder et al. v. W. A. Gayle et al., No. 1147; U.S. District Court for the Northern (Montgomery) Division of the Middle District of Alabama. (1839 - ); Records of District Courts of the United States, 1685 - 1991; Record Group 21; National Archives.
Explore further with Teaching With Documents: The Arrest Records of Rosa Parks, also from the National Archives. Parks recalled her role in Montgomery Bus Boycott in a brief interview (Teachers' Domain; 2 min., 13 sec).