The Kingdom of Sardinia was a state in Southern Europe which existed from the early 14th until the mid-19th century. It was the predecessor state of today's Italy.

When it was acquired by the Duke of Savoy in 1720, it was a small state with weak institutions. However, the Savoyards united it with their possessions on the Italian mainland and, by the time of the Crimean War in 1853, had built the resulting kingdom into a strong power. The country was sometimes called Savoy-Sardinia in this period and often called Piedmont-Sardinia or just Piedmont by modern French historians. Its final capital was Turin, the capital of Savoy since the Middle Ages.

The kingdom 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 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 it was ceded by the Habsburg and Bourbon claimants to the Spanish throne to Duke Victor Amadeus II of Savoy. The kingdom of Sardinia came to be progressively identified with the entire domain ruled by the House of Savoy, which included, besides Savoy and Aosta, dynastic possessions since the 11th century, the Principality of Piedmont (a possession built up in the 13th century), and the County of Nice (a possession since 1388). While in theory the traditional capital of the island of Sardinia and seat of its viceroys was Cagliari, the Piedmontese city of Turin was the de facto capital of Savoy.

When the mainland domains of the House of Savoy were occupied and eventually annexed by Napoleonic France, the king of Sardinia made his permanent residence on the island for the first time in its history. 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. In 1847–48, in a "perfect fusion", the various Savoyard states were unified under one legal system, with the capital in Turin, and granted a constitution, the Statuto Albertino. 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.