The Montgomery bus boycott was a political and social protest campaign against the policy of racial segregation on the public transit system of Montgomery, Alabama. It was a foundational event in the civil rights movement in the United States. The campaign lasted from December 5, 1955—the Monday after Rosa Parks, an African-American woman, was arrested for her refusal to surrender her seat to a white person—to December 20, 1956, when the federal ruling Browder v. Gayle took effect, and led to a United States Supreme Court decision that declared the Alabama and Montgomery laws that segregated buses were unconstitutional.

A boycott is an act of nonviolent, voluntary abstention from a product, person, organization, or country as an expression of protest. It is usually for moral, social, political, or environmental reasons. The purpose of a boycott is to inflict some economic loss on the target, or to indicate a moral outrage, usually to try to compel the target to alter an objectionable behavior.