The Duchy of Savoy (Ducato di Savoia; Duché de Savoie) was a territorial entity of the Savoyard state that existed from 1416 until 1860 and was a possession of the House of Savoy.
It was created when Sigismund, Holy Roman Emperor, raised the County of Savoy into a duchy for Amadeus VIII. The duchy was an Imperial fief, subject of the Holy Roman Empire, until 1792, with a vote in the Imperial Diet. From the 16th century, Savoy belonged to the Upper Rhenish Circle.
Its territory included the current French departments of Savoie, Haute-Savoie, and the Alpes-Maritimes, the current Italian region of Aosta Valley, a large part of Piedmont and the County of Geneva in Switzerland, which was then lost to the Old Swiss Confederacy. The main Vulgar languages that were spoken within the Duchy of Savoy were Piedmontese and Arpitan.
The Duchy of Savoy was the central and most prominent of the territories possessed by the House of Savoy, and hence this title was and still is used often to indicate the whole of their possessions. In reality, the Savoys ruled not a unitary state, but a complex array of different entities and titles with different institutional, cultural, and legal backgrounds. These included for example the Duchy of Aosta, Principality of Piedmont, and county of Nice, which were distinct and not juridically part of the Duchy of Savoy. The Savoys themselves referred to their possessions as a whole as "the States of the Duke of Savoy" (Italian: "gli Stati del Duca di Savoia"). Today, historians use the term Savoyard state to indicate this entity, which is an example of composite monarchy where many different and distinct territories are united in a personal union by having the same ruler.
The Duchy was created in 1416 when Sigismund, Holy Roman Emperor (1433–1437) awarded the title of "Duke" to Count Amadeus VIII.
Being landlocked at its conception in 1388, the then-County of Savoy acquired a few kilometres of coastline around Nice. Other than this expansion, the 14th century was generally a time of stagnation.