Lord Stanley

Earldom of Derby
Arms of Stanley, Earls of Derby: Argent, on a bend azure three buck's heads cabossed or.
Creation date	1139 (first creation)
Monarch	Stephen, King of England
Peerage	Peerage of England
First holder	Robert de Ferrers, 1st Earl of Derby (first creation)
Present holder	Edward Stanley, 19th Earl of Derby
Heir apparent	Edward John Robin Stanley, Lord Stanley
Subsidiary titles	Lord Stanley Baron Stanley of Bickerstaffe
Seat(s)	Knowsley Hall
Armorial motto	Sans changer (Without changing)

Earl of Derby (/ˈdɑːbi/ DAR-bi) is a title in the Peerage of England. The title was first adopted by Robert de Ferrers, 1st Earl of Derby under a creation of 1139. It continued with the Ferrers family until the 6th Earl forfeited his property toward the end of the reign of Henry III and died in 1279. Most of the Ferrers property and, by a creation in 1337, the Derby title, were then held by the family of Henry III. The title merged in the Crown upon Henry IV's accession to the throne.

It was created again for the Stanley family in 1485. Lord Derby's subsidiary titles are Baron Stanley of Bickerstaffe in the County Palatine of Lancaster (created 1832), and Baron Stanley of Preston, in the County Palatine of Lancaster (1886). The 1st to 5th Earls also held an earlier Barony of Stanley, created for the 1st Earl's father in 1456 and currently abeyant; the 2nd to 5th Earls held the Barony of Strange created in 1299, currently held by the Viscounts St Davids; and the 7th to 9th Earls held another Barony of Strange, created in error in 1628 and currently held independently of other peerages.

The courtesy title of the heir apparent is Lord Stanley.

Several successive generations of the Stanley Earls, along with other members of the family, have been prominent members of the Conservative Party, and at least one historian has suggested that this family rivals the Cecils (Marquesses of Salisbury) as the single most important family in the party's history. They were at times one of the richest landowning families in England.