We look at 11 players who played for both sides.
Ahead of Saturday's Sky Bet Championship Play-Off semi-final first leg between Leeds United and Frank Lampard's Derby County at Pride Park, we look at 11 players who have played for both the Whites and the Rams...
The goalkeeper came through the youth ranks at Leeds and has been with Derby since 2015, making over 150 appearances for the club.
The full-back helped United win the 1991/92 First Division Championship. He joined the Rams after a spell with Italian outfit Torino.
Former England international Warnock spent time at Leeds from 2013-2015 before departing to Pride Park. He went onto have spells at Wigan Athletic, Burton Albion and Bradford City before retiring.
Signed from Plymouth Argyle, Conolly went on to captain the Rams. The defender joined Leeds from Derby on a free transfer following our promotion back to the Sky Bet Championship in 2010.
Signed from Charlton Athletic in 1999, Mills went on to play for the Whites in the Champions League. He joined Manchester City in 2004, from whom he had a loan spell at Derby.
Derby signed the midfielder from Doncaster Rovers in 2008 and he joined Leeds from Pride Park four years later. He went onto have stints at Ipswich Town, Rotherham United, Oldham Athletic and now Crewe Alexandra.
United paid a reported £7m to sign Johnson from Derby in 2001. Injuries hampered a four year spell with the Whites and he moved back to the Rams in 2005.
The forward joined Derby after a loan spell in 2008. He spent a lot of his time out on loan from Pride Park before leaving to join Portsmouth. Varney joined Leeds in 2012 and is now at Cheltenham Town.
The striker's goals helped Leeds reach the Sky Bet Championship Play-Off Final in 2006. He joined Sheffield United in the next transfer window, before moving to Pride Park two years later.