One of the hereditary judgeships into which Sardinia was divided in the middle ages;
- A modern Italian province.
The city of Cagliari, today the capital of Sardinia, is in the south of the island, on the Gulf named after it.
The judgeships appeared in Sardinia in the 9th century and continued even after Pisa became the principal power in the island in the 11th century. The Cagliari judgeship was held separately until 1258, when the last independent judge ceded his territory to Genoa, the great rival of Pisa.
Pisa however prevailed and the judgeship was divided between two of the other judges, those of Gallura and Arborea, and a Pisan family, the Gherardeschi, extinct in 1355. The divided office was simply titular after 1258. Pisa withdrew from Cagliari, its last town in Sardinia, in 1326 and Aragon took it over.
The province of Cagliari in present-day Italy is the southern quarter of the island.