The "Letter from Birmingham Jail", also known as the "Letter from Birmingham City Jail" and "The Negro Is Your Brother", is an open letter written on April 16, 1963, by Martin Luther King Jr. It says that people have a moral responsibility to break unjust laws and to take direct action rather than waiting potentially forever for justice to come through the courts. Responding to being referred to as an "outsider", King writes: "Injustice anywhere is a threat to justice everywhere."

The letter, written in response to "A Call for Unity" during the 1963 Birmingham campaign, was widely published, and became an important text for the civil rights movement in the United States. The letter has been described as "one of the most important historical documents penned by a modern political prisoner", and is considered a classic document of civil disobedience.