An experienced defender
This move may come as a surprise to many as Davies made 29 appearances for Hull last season and has been an important figure for them over the last four years.
He made a total of 123 appearances in all competitions in his spell for the Tigers, notching up four goals in the process.
Whilst at Birmingham, he found the back of the net 11 times in his 89 appearances - an impressive statistic for a defender.
Derby manager Garry Rowett will be hoping that Davies can bring vital quality and experience to the Rams' defence ahead of next season.
This signing will also raise doubts over the future of the likes of Richard Keogh and Jason Shackell and raise questions as to whether they may be allowed to leave the club this summer.
A new challenge
At 32 years old, this is likely to be the last 'big' move of Davies' career, and he will be hoping that it turns out to be a successful one.
He told Derby's official site that the current Rams squad "is capable of promotion or at least the play-offs" and that at his age "people start thinking that you want to wind down and look for a bit of security but that is not the case with me."
Derby were arguably one of the biggest underachievers in the Championship last season, with a host of managerial changes not helping matters.
They began the season under the management of Nigel Pearson before Steve McClaren's return turned out to be an unsuccessful one.
This led to Rowett being appointed as manager before the end of the season with the long-term objective of getting the club back in to the top -light.
They will be hoping that this particular signing, reported to be around the £500,000 mark, will help them improve on their ninth-placed finish in the league last season which left them 13 points adrift of the play-off places.