The (Pactum) Ludovicianum (also spelled Ludowicianum or Hludowicianum) was an agreement reached in 817 between the Emperor Louis the Pious (“Ludovicus Pius”) and Pope Paschal I concerning the government of central Italy and the relation of the Papal States to the Carolingian Empire.
Certain sections of the Ludovicianum are thought to be confirmations of agreements made between Louis's father, Charlemagne, and Pope Hadrian I during the former's trips to Rome in 781 and 787.
The negotiations which resulted in the Ludovicianum began during the pontificate of Stephen IV, but the agreement was only concluded shortly after the election of his successor, Paschal I, in January 817.
The text of the Ludovicianum closely resembles the later Pactum Ottonianum between Emperor Otto the Great and Pope John XII (962).
A manuscript fragment that also closely resembles the Ludovicianum and may in fact be a copy of it survives from the ninth or early tenth century, and was first published by Angelo Mercati in 1926.