Derby have signed defender Tyrone Mears from West Ham for £1m.
Mears impressed during a loan spell at Derby
The 24-year-old had been on loan at Pride Park from January and was a member of the team that won the Championship play-off final.
He has signed a three-year contract with the Rams and boss Billy Davies said: "We're delighted with this deal.
"Tye is a very good young full back with excellent pace and potential. We need him for the challenge ahead and I know he is committed to working hard."
Mears started his career at Manchester City before moving to Preston in July 2002.
While at Deepdale he played under Davies but was sold to West Ham for £1m in July 2006.
However, Mears failed to make the first-team breakthrough at the Hammers, starting just three Premier League matches.
Mears becomes Derby's second close-season signing following the purchase of Robert Earnshaw from Norwich.