An open letter is a letter that is intended to be read by a wide audience.

They usually take the form of a letter addressed to an individual that is also provided to the public through newspapers and other media. Especially common are critical open letters addressed to political leaders. Letters patent are another form of open letter in which a legal document is both mailed to a person by the government, and publicized so that all are made aware of it. Open letters can also be addressed directly to a group rather than any individual.

Notable open letters

• Many of the epistles of the Bible are open letters
• J'accuse by Émile Zola over the Dreyfus Affair
• Martin Luther King's Letter from Birmingham Jail
• Bill Gates's Open Letter to Hobbyists attacking software piracy