Experienced midfielder John Eustace has become Derby's fifth summer signing after impressing during a trial spell.
The 33-year-old has penned a one-year deal with the club after spending pre-season with Nigel Clough's men following his departure from Watford.
The move sees a return to Pride Park for Eustace, who made nine appearances during a loan spell at the end of the 2008/09 season.
Clough told the club's official website: "We're very happy to sign John and it's no secret we've tried to bring him here permanently on a few occasions in the past.
"He's got good experience and he's a type of player we haven't had in the squad for a while, so he'll be vital both on and off the pitch.
"He'll be very good for our midfielders as well, he's got bags of experience and that will only help them improve as players too."