a cadet branch of the house of Plantagenet (Plantagenet, house of) (q.v.). In the 15th century, it provided three kings of England—Henry IV, Henry V, and Henry VI—and, defeated by the house of York (York, house of) (q.v.), passed on its claims to the Tudor dynasty.

The family name first appeared in 1267, when the title earl of Lancaster was granted to Edmund “Crouchback” (1245–96), the youngest son of Henry III. Two of Edmund's sons by his second wife, Blanche of Artois, succeeded to the title: Thomas, Earl of Lancaster (d. 1322), and Henry, Earl of Lancaster (d. 1345). Henry's son, Henry, 1st Duke of Lancaster (d. 1361), was survived only by two coheiresses. The elder daughter, Maud, married to William, duke of Bavaria, died without issue a year after her father. The Lancastrian inheritance thus fell to the younger daughter, Blanche, and to her husband, John of Gaunt (d. 1399), third surviving son of Edward III. After Gaunt's death his son Henry of Lancaster deposed Richard II and became king himself, as Henry IV. On his accession the duchy of Lancaster was merged in the crown, and the house of Lancaster, in the persons of Henry IV, Henry V, and Henry VI, ruled England for more than 60 years.

Henry V alone had the strength to rule; and his marriage to the daughter of the mad King Charles VI of France did not improve his son's chances. Henry IV had founded his title to the throne on the descent of Lancaster from Henry III in order to avoid the greater claim of the heirs of Gaunt's elder brother Lionel, Duke of Clarence; in the end his grandson was defeated by Edward IV of the house of York—the heir both of Clarence and of Gaunt's younger brother Edmund, Duke of York.

The last remaining fragment of Lancastrian title was that which Henry VII derived through Gaunt's legitimized bastard line, the Beaufort Family. By the time Henry VII had inaugurated the Tudor monarchy, the Lancaster lands were firmly in the hands of the crown.