The Kingdom of Sardinia, also referred to as the Kingdom of Savoy-Sardinia, Piedmont-Sardinia, or Savoy-Piedmont-Sardinia during the Savoyard period, was a state in Southern Europe from the early 14th until the mid-19th century.

The Kingdom was a member of the Council of Aragon and initially consisted of the islands of Corsica and Sardinia, sovereignty over both of which was claimed by the Papacy, which granted them as a fief, the regnum Sardiniae et Corsicae ("kingdom of Sardinia and Corsica"), to King James II of Aragon in 1297. Beginning in 1324, James and his successors conquered the island of Sardinia and established de facto their de jure authority. In 1420, after the Sardinian–Aragonese war, the last competing claim to the island was bought out. After the union of the crowns of Aragon and Castile, Sardinia became a part of the burgeoning Spanish Empire.

In 1720, the island was ceded by the Habsburg and Bourbon claimants to the Spanish throne to the Duke of Savoy Victor Amadeus II. The Savoyards united it with their historical possessions on the Italian mainland, and the Kingdom came to be progressively identified with the Mainland states, which included, besides Savoy and Aosta, dynastic possessions like the Principality of Piedmont and the County of Nice, over both of which the Savoyards had been exercising their control since the 13th century and 1388, respectively.

The formal name of this composite state was the "States of His Majesty the King of Sardinia" and is referred to as either Savoy-Sardinia, Piedmont-Sardinia, or even the Kingdom of Piedmont, since the island of Sardinia had always been of secondary importance to the monarchy. Under Savoyard rule, the Kingdom's government, ruling class, and center of population were entirely situated in the Mainland. Therefore, while the capital of the island of Sardinia and the seat of its viceroys had always been de jure Cagliari, it was the Piedmontese city of Turin, the capital of Savoy since the mid 16th century, which was the de facto seat of power. This situation would be conferred official status with the Perfect Fusion of 1847, when all the Kingdom's governmental institutions would be centralized in Turin.

When the Mainland domains of the House of Savoy were occupied and eventually annexed by Napoleonic France, the king of Sardinia temporarily resided on the island for the first time in Sardinia's history under Savoyard rule. The Congress of Vienna (1814–15), which restructured Europe after Napoleon's defeat, returned to Savoy its Mainland possessions and augmented them with Liguria, taken from the Republic of Genoa. Following Geneva’s accession to Switzerland, the Treaty of Turin (1816) transferred Carouge and adjacent areas to the newly-created Swiss Canton of Geneva. In 1847–48, through an act of Union analogous to the one between Great Britain and Ireland, the various Savoyard states were unified under one legal system with their capital in Turin, and granted a constitution, the Statuto Albertino.

By the time of the Crimean War in 1853, the Savoyards had built the kingdom into a strong power. There followed the annexation of Lombardy (1859), the central Italian states and the Two Sicilies (1860), Venetia (1866), and the Papal States (1870). On 17 March 1861, to more accurately reflect its new geographic extent, the Kingdom of Sardinia changed its name to the Kingdom of Italy, and its capital was eventually moved first to Florence and then to Rome. The Savoy-led Kingdom of Piedmont-Sardinia was thus the legal predecessor of the Kingdom of Italy, which in turn is the predecessor of the present-day Italian Republic.