Here's a statement from the club...
France international Mathieu Debuchy has joined Arsenal Football Club on a long-term contract for an undisclosed fee.
The 28-year-old right back has just returned from the World Cup in Brazil, where he helped France reach the quarter-finals.
An experienced defender, Debuchy arrives from Newcastle United, where he featured 46 times during an 18-month spell. He spent the first nine years of his senior career with French side Lille, where he made 233 Ligue 1 appearances for his boyhood club and a further 18 in the Uefa Champions League.
Debuchy helped Lille to a league and Coupe de France double in 2010/11 and in the following season his contribution was recognised by being named in the 2011/12 Ligue 1 Team of the Season. His performances also earned him his international debut against Albania in October 2011, and he now has 25 caps for France.
Arsène Wenger said: "We are delighted to welcome Mathieu Debuchy to Arsenal Football Club. He has shown he can perform at the highest level with his club sides and also for France. He is a quality defender who has good Premier League experience and I'm confident he will fit in very well with us."
Debuchy will join up with his new team-mates soon for pre-season preparations and is expected to make his debut at the Emirates Cup in the first weekend of August.
He said: "I'm very proud to be joining a great club like Arsenal and to wear its colours, it's one of the biggest clubs in the whole world. I'm looking forward to working with Arsène Wenger and to helping the team build on last season's FA Cup success. Playing again in the Champions League is a big excitement for me and I will do my best to help Arsenal compete for trophies."
Debuchy's Arsenal squad number will be revealed soon through Arsenal's official Instagram account @Arsenal.
Everyone at Arsenal would like to welcome Mathieu to the Club.