two American Appalachian mountaineer families who, with their kinfolk and neighbours, engaged in a legendary feud that attracted nationwide attention in the 1880s and '90s and prompted judicial and police actions, one of which drew an appeal up to the U.S. Supreme Court (1888).

The Hatfields were headed by William Anderson (“Devil Anse”) Hatfield (1839–1921), and the McCoys by Randolph (“Rand'l”) McCoy (1839?–1921), each of whom fathered 13 children (some sources claim 16 for McCoy). The families lived on opposite sides of a border stream, the Tug Fork—the McCoys in Pike county, Kentucky, and the Hatfields in Logan county (or Mingo county, formed from a portion of Logan county in 1895), West Virginia. Each had numerous kinfolk and allies in the respective counties in which they lived.

The origins of the feud are obscure. Some attribute it to hostilities formed during the American Civil War, in which the McCoys were Unionists and the Hatfields were Confederates, others to Rand'l McCoy's belief that a Hatfield stole one of his hogs in 1878. However, although animosities had built up and occasional fights had broken out, the first major bloodletting did not occur until 1882, when Ellison Hatfield was mortally shot in a brawl with McCoys and, in revenge, the Hatfields kidnapped and executed three McCoy brothers—Tolbert, Phamer, and Randolph, Jr.

These murders sharpened the backwoods warfare, and thereafter Hatfields and McCoys repeatedly ambushed and killed one another. Hatfields arrested in their home county and McCoys arrested in their home county were invariably released or acquitted of their deeds because of their respective local support and influence. Fighting reached a climax in 1888. On New Year's Day a group of Hatfields led by Jim Vance attacked the home of patriarch Rand'l McCoy, missing him but shooting dead a son and a daughter and burning his houses. In retaliation, a posse of McCoys and neighbours, headed by a Pike County deputy sheriff, made successive raids across the border into West Virginia, killing Vance and at least three others, battling with a West Virginia posse, and eventually rounding up nine of the Hatfield clan for indictment and trial in Kentucky. West Virginia filed suit in federal court, charging kidnapping and lawlessness; Kentucky defended the abduction; and newspapers all over the country began carrying front-page stories of the feud and sending in reporters. Finally, in May 1888, a divided U.S. Supreme Court ruled (in Plyant Mahon v. Abner Justice, jailer of Pike County, Ky.) that Kentucky had the legal right to detain the accused for trial. The trials, later in the year, resulted in one sentence of death by hanging and eight sentences of imprisonment.

Although there were flare-ups thereafter, notably in 1896–97, the feuding gradually abated and had ended by the second decade of the 20th century. The Hatfield-McCoy legend was embellished by a brief love affair about 1880 between Johnson (“Johnse”) Hatfield and Rose Anna McCoy—an affair that was opposed and eventually broken up by the McCoys. Newspapers turned it into a Romeo-and-Juliet romance.