Arnulf of Carinthia (German: Arnulf von Kärnten) (850 – December 8, 899) was one of the last ruling members of the Carolingian Dynasty in East Francia, which had been split from the rest of Frankish territory by the Treaty of Verdun in 843. He was the illegitimate son of the Bavarian king Carloman and his concubine, Liutswind (also Litwinde or Litwindie), of Carinthian origin, daughter of one Count Ernst. He was given the duchy of Carinthia (a Frankish vassal state and successor of the ancient Principality of Karantania) by his father when he divided his realm, giving Bavaria to Louis the Younger and Italy to Charles the Fat, in 880 on his death.

He spent his childhood in Karantania, homeland of his mother. Carloman had a court there, in Moosburg (then Blatograd), where the young Arnulf grew up. From later events it is evident that the Karantanians, from an early time, treated him as their own duke.

He took the leading role in the deposition of his uncle, the Emperor Charles the Fat. With the support of the nobles, Arnulf assumed his title of King of East Francia (later Germany) in 887. Charles asked only for a few royal villas in Swabia, which Arnulf granted him.

Arnulf was not a negotiator, but a fighter. At the decisive Battle of Leuven on September 891, he defeated an invading force of the Northmen, or Vikings, essentially ending invasion attempts on that front. The Annales Fuldensis (Annals of Fulda) report that the bodies of dead Northmen blocked the run of the river. After his victory, Arnulf had built a new castle on an island in the Dijle river (Latin Luvanium, local Lovon).

In 894 or 895, Great Moravia probably lost a part of its territory — present-day Western Hungary — to him. Arnulf, however, failed to conquer Great Moravia in 892, 893, and 899. In 895, Bohemia broke away from Great Moravia and became his vassal. An accord was made between him and the Bohemian Duke Borivoj (reigned 870-895); Bohemia was freed from the danger of invasion.

Arnulf invaded Italy in 896 and was crowned Emperor and King of Italy by Pope Formosus (pope 891-896) in opposition to Lambert of Spoleto. He only retained power in Italy as long as he was personally there, he was vigourously opposed by Lambert's mother, Agiltrude, and when he left, having taken ill, most of Italy was in Lambert's supporters' hands. On his death in 899, he was succeeded as a king of the East Franks by his son by his wife Ota, Louis the Child (900-911).
Arnulf's illegitimate son Zwentibold reigned as king of Lotharingia from 895 to 900.