Micajah "Big" Harpe, born Joshua Harper (before 1768 – August 24, 1799), and Wiley "Little" Harpe, born William Harper (before 1770 – February 8, 1804), were American murderers, highwaymen and river pirates who operated in Tennessee, Kentucky, Illinois and Mississippi in the late 18th century. They are often considered the earliest documented serial killers in the United States history.

Loyal to the British Crown during the American Revolution, the Harpes became outlaws after the war and began robbing and killing settlers in the remote frontier west of the Appalachian Mountains. They are believed to have killed 39 people, and possibly as many as 50. As the Harpes' crimes gained notoriety, vigilante groups formed to avenge their victims, and they were eventually tracked down and executed around the turn of the century. Their savagery has since entered American folklore, appearing to have been motivated more by blood lust than financial gain.