The Welfs were a Bavarian dynasty so named because many of its members were named Welf.

The first known member is 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 Henries of the Welf dynasty.

Henry the Proud, duke of Bavaria and also of Saxony, was the favoured candidate in the imperial election against the Hohenstaufens. He was defeated in the election and was dispossessed of his duchies.

Henry the Lion recovered his father's two duchies. 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 England 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 to the imperial throne under the name Otto IV.

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