The title Baron Bergavenny (or Abergavenny) was created several times in the Peerage of England and once in the Peerage of Great Britain, all but the first being baronies created by error.
The feudal barony of Abergavenny came into existence shortly after the Norman Conquest of 1066. The barony by writ was first created in 1392 for Sir William de Beauchamp, a younger son of the 11th Earl of Warwick. This creation passed to his son, who succeeded as 2nd Baron, and who was subsequently created Earl of Worcester. On his death, the Earldom of Worcester became extinct, but the Barony passed to his daughter, who by modern doctrine succeeded as 3rd Baroness. She died in 1447, when the Barony descended to her son, who succeeded as 4th Baron.
In 1450, however, Sir Edward Nevill, widower of the 3rd Baroness, was summoned to Parliament as Lord Bergavenny. It has been assumed that this summons was intended to be in right of his wife, but as she was already dead and the Barony was already vested in her son by Nevill, by modern doctrine this served to create a new Barony by Writ. This second creation merged with the first creation in 1476, when the 1st Baron died and his son, the aforementioned 4th Baron of the first creation, also became 2nd Baron of the second creation.
In 1587, on the death of the 6th Baron (of the first creation) and 4th Baron (of the second creation), by modern doctrine both Baronies descended to his daughter, Mary, Lady Fane, wife of Sir Thomas Fane, who thus became de jure 7th and 5th Baroness. The title (for it was believed at the time only to be one Barony) was claimed by Edward Nevill, the heir male of the 4th and 2nd Baron, and in 1604 he was summoned to Parliament as Lord Bergavenny. As he was not entitled to either of the existing Baronies, this served to create a further Barony by Writ. By modern doctrine, the first and second creations descended to the Earls of Westmorland, heirs of the 7th and 5th Baroness, until both became abeyant on the death of the 7th Earl (and 14th and 12th Baron) in 1762.