The significance of the Montgomery Bus Boycott lies in its role as a pivotal event in the American civil rights movement. Sparked by Rosa Parks' refusal to give up her seat to a white man in December 1955, the boycott began as a protest against racial segregation on public buses in Montgomery, Alabama. It lasted for over a year and involved the African American community refusing to use the bus system. The boycott brought national attention to the issue of racial discrimination and led to a Supreme Court ruling declaring bus segregation unconstitutional, setting a precedent for further civil rights activism.