The Honour of Lancaster was a medieval English honour (a large feudal lordship containing several different fiefs), located primarily in the north-west of England. It began as the fief granted by William the Conqueror to Roger the Poitevin after the Norman conquest in 1066. This included the lands between the River Ribble and the River Mersey, as well as the district of Amounderness, north of the Ribble.
After Roger lost his English lands the honour was given to various members of the royal family and eventually came into the hands of Edmund Crouchback, who was a son of King Henry III. It remained the possession of his heirs until one of them, Henry Bolingbroke, became king of England as Henry IV. Since then the honour has been a possession of the ruling monarch.