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."

An open letter is a letter that is intended to be read by a wide audience, or a letter intended for an individual, but that is nonetheless widely distributed intentionally.