The Norman conquest of southern Italy lasted from 999 to 1139, involving many battles and independent conquerors. In 1130, the territories in southern Italy united as the Kingdom of Sicily, which included the island of Sicily, the southern third of the Italian Peninsula (except Benevento, which was briefly held twice), the archipelago of Malta, and parts of North Africa.

Itinerant Norman forces arrived in southern Italy as mercenaries in the service of Lombard and Byzantine factions, communicating news swiftly back home about opportunities in the Mediterranean. These groups gathered in several places, establishing fiefdoms and states of their own, uniting and elevating their status to de facto independence within 50 years of their arrival.

Unlike the Norman conquest of England (1066), which took a few years after one decisive battle, the conquest of southern Italy was the product of decades and a number of battles, few decisive. Many territories were conquered independently, and only later were unified into a single state. Compared to the conquest of England, it was unplanned and disorganised, but equally complete.