The Welfs were a Frankish dynasty so named because many of its members were named Welf. They initially arrived and settled in northern Italy during the times of Charlemagne.

The first member of the family named Welf was Welf I, father of Judith, the wife of the emperor Louis the Pious, and of Emma, the wife of Louis the German. The two sons of Welf I, brothers of Judith and Emma, were Conrad and Rudolph. Conrad was the ancestor of the counts of Burgundy.

Welf II was a count in Germany and Bavaria.

Welf V married countess Matilda of Tuscany who died childless and left him her possessions in Saint-Siège: Tuscany, Ferrara, Modena, Mantua, Reggio, etc., which led to the Investiture controversy.

Henry the Black , duke of Bavaria from 1120-1126, was the first of the three Henrys of the Welf dynasty.

Henry the Proud, duke of Bavaria and also of Saxony, was the favoured candidate in the imperial election against Conrad III of the Hohenstaufens. He lost the election, as the other princes feared his power and temperament, and was dispossessed of his duchies by Conrad III.

Henry the Lion recovered his father's two duchies, Saxony in 1142, Bavaria in 1156. In 1158 he married Matilda, Duchess of Saxony (1156-1189), the daughter of Henry II of England and Eleanor of Aquitaine and sister of Richard Lionheart. Dispossessed of his duchies after the Battle of Legnano in 1176 by Emperor Frederick I and the other princes of the German Empire eager to claim parts of his vast territories, he was exiled to the court of his father-in-law Henry II in Normandy in 1180, returned to Germany three years later as duke of a much reduced realm around Brunswick, and died there in 1195.

His son Otto of Brunswick was elected elected king and crowned emperor as Otto IV.

In Italy the partisans of the Welfs were known as Guelphs.

The Welfs of Brunswick-Lüneburg continued to rule in that area until the fall of the German monarchies in 1918. In 1692 the head of the cadet Calenberg line was raised to the status of an imperial Elector, and became known as the Elector of Hanover. His son, Georg Ludwig, inherited the British throne in 1714 as a result of the Act of Settlement 1701. Members of the Welf or Hanoverian dynasty continued to rule in Britain until the death of Queen Victoria in 1901. Hanover itself was raised to a Kingdom in 1814, but was annexed by Prussia following the Austro-Prussian War of 1866, in which Hanover had sided with Austria. The senior line of the dynasty ruled the much smaller Duchy of Brunswick-Wolfenbüttel . This line became extinct in 1884. Although the Duchy should have been inherited by the Duke of Cumberland, son of the last King of Hanover, suspicions of his loyalty led the duchy's throne to remain vacant until 1913, when Cumberland's son married the daughter of Kaiser Wilhelm II and was allowed to inherit the duchy. His rule there was short-lived, however, as the monarchy came to an end following the First World War in 1918.

The Welf dynasty continues to exist, however. Its current head, named, like many of his ancestors, Ernst August, is most famous as the third and present husband of Princess Caroline of Monaco.