A message in a bottle (MIB), message bottle, or bottled message is a form of communication in which a message is sealed in a container (typically a bottle) and released into a conveyance medium (typically a body of water).

Messages in bottles have been used to send distress messages; in crowdsourced scientific studies of ocean currents; as memorial tributes; to send deceased loved ones' ashes on a final journey; to convey expedition reports; and to carry letters or reports