|House of Wettin|
|Final ruler||Multiple sovereigns until 1918|
|Current head||Prince Michael, titular Grand Duke of Saxony|
|Founding year||AD 900s|
|Cadet branches||In order of seniority:
Saxe-Weimar-Eisenach (Grand Duchy of Saxony)
Saxe-Coburg and Gotha
Electorate/Kingdom of Saxony
The House of Wettin is a dynasty of German counts, dukes, prince-electors (Kurfürsten) and kings that once ruled the area of today's German states of Saxony, the Saxon part of Saxony-Anhalt, and Thuringia for more than 800 years as well as holding at times the kingship of Poland. Agnates of the House of Wettin have, at various times, ascended the thrones of Great Britain, Portugal, Bulgaria, Poland, Saxony, and Belgium; of these, only the British and Belgian lines retain their thrones today. (See list of members.)
The oldest member of the House of Wettin who is known for certain was Thiedericus (died 982), who was probably based in the Liesgau (located at the western edge of the Harz). Around 1000, as part of the German conquest of Slavic territory, the family acquired Wettin Castle, after which they named themselves. Wettin Castle is located in Wettin in the Hosgau on the Saale River. Around 1030, the Wettin family received the Eastern March as a fief. 
The prominence of the Wettin family in the Slavic marches caused Emperor Henry IV to invest them with the March of Meissen as a fief in 1089. The family advanced over the course of the Middle Ages: in 1263 they inherited the landgraviate of Thuringia (though without Hesse), and in 1423 they were invested with the Duchy of Saxony, centred at Wittenberg, thus becoming one of the prince-electors of the Holy Roman Empire.
The family divided into two ruling branches in 1485 when the sons of Frederick II, Elector of Saxony divided the territories hitherto ruled jointly.
The elder son Ernest, who had succeeded his father as Prince-elector, received the territories assigned to the Elector (Electoral Saxony) and Thuringia, while his younger brother Albert obtained the March of Meissen, which he ruled from Dresden. As Albert ruled under the title of "Duke of Saxony", his possessions were also known as Ducal Saxony.
The older, Ernestine branch remained predominant until 1547 and played an important role in the beginnings of the Protestant Reformation. Their predominance ended in the Schmalkaldic War, which pitted the Protestant Schmalkaldic League against Emperor Charles V. Although itself Protestant, the Albertine branch rallied to the Empire's cause; Charles V rewarded them by forcing the Ernestines to sign away their rights to the Electoral title and lands to the Albertines. The Ernestine line was thereafter restricted to Thuringia, and its dynastic unity swiftly crumbled.
The Albertine Wettin maintained most of the territorial integrity of Saxony, preserving it as a significant power in the region, and using small appanage fiefs for their cadet branches, few of which survived for significant lengths of time. The Ernestine Wettin, on the other hand, repeatedly subdivided their territory, creating an intricate patchwork of small duchies and counties in Thuringia.
The junior Albertine branch ruled as Electors (1547–1806) and Kings of Saxony (1806–1918) and also played a role in Polish history: two Wettin were Kings of Poland (between 1697–1763) and a third ruled the Duchy of Warsaw (1807–1814) as a satellite of Napoleon. After the Napoleonic Wars, the Albertine branch lost about 40% of its lands, including the old Electoral Saxony, to Prussia, restricting it to a territory coextensive with the modern Saxony).
The senior Ernestine branch lost the electorship to the Albertine in 1547, but retained its holdings in Thuringia, dividing the area into a number of smaller states. One of the resulting Ernestine houses, that of Saxe-Coburg and Gotha, went on to contribute kings of Belgium (from 1831) and Bulgaria (1908 - 1946), as well as furnishing consorts to queens regnant of Portugal (Ferdinand II of Portugal) and the United Kingdom (Prince Albert, husband of Queen Victoria), as well as to Maximilian I of Mexico (Carlota of Mexico, the first Belgian princess). As such, the British, Portuguese, and for a time, Mexican, thrones became a possession of persons who belonged to the House of Wettin.
From George I to Queen Victoria, the British Royal family was variously called Hanover, Brunswick and Guelph. In the late 19th century, Queen Victoria charged the College of Heralds in England to determine the correct personal surname of her late husband, Prince Albert of Saxe-Coburg and Gotha - and, thus, the proper surname of the Royal Family upon the accession of her son. After extensive research they concluded that it was Wettin, but this name was never used, either by the Queen or by her son or grandson, Edward VII and George V of the United Kingdom; they were simply called 'Saxe-Coburg-Gotha'.
Severe anti-German sentiment during World War I led some influential members of the public to quietly question the loyalty of the Royal Family, because they had a German or German-sounding name. By order-in-council, the name of the British royal family was legally changed to Windsor, prospectively for all time.
When Queen Elizabeth II ascended the throne in 1952, a question arose as to whether the royal family's name would change after her to 'Mountbatten' - the name adopted by the Queen's husband, Prince Philip of Greece and Denmark, from his mother's family ('Battenberg' translated to English). The reply from Buckingham Palace was immediate that the Royal Family's name would remain "Windsor" in perpetuity. However, the Queen issued an order in 1957, which provides that those of her descendants who do not reign and have no other title may use the surname "Mountbatten-Windsor".