Norwich City have completed the signing of goalkeeper Jake Kean following his release from Blackburn Rovers.
Paul Anderson has become Bradford's seventh signing of the summer, agreeing terms on a two-year deal with the Bantams.
The 28-year-old, signed from Ligue 1 side Lorient in summer 2010, has forged a strong partnership with Per Mertesacker in the centre of the Gunners' defence, helping return 15 clean sheets in his 31 Barclays Premier League appearances as the team secured fourth place and also reached the FA Cup final.
"I am very proud to have reached agreement with the club on a new contract," Koscielny said on the club's official website, www.arsenal.com.
"I have enjoyed four great years at Arsenal already, and I look forward to continuing to help the team in the years to come."
Manager Arsene Wenger added: "Laurent has proven himself to be an outstanding player since joining us in 2010 and has showed his quality once again this season. I am delighted he has decided to commit his future to the club."