Arsenal have signed defender Laurent Koscielny from French side Lorient.
The 24-year-old moves to north London on a long-term contract for an undisclosed fee, the Premier League club announced.
Manager Arsene Wenger told Arsenal's official website: "Koscielny is a central defender with great ability who performed extremely well last season for Lorient.
"We identified him as a very strong centre-half, who has made big progress very quickly. He has shown he is mentally strong, he's a fighter and a very strong competitor. Koscielny is a great addition to our squad."
Koscielny, who will wear the number six shirt, is set to make his first appearance for Arsenal at the Emirates Cup at the end of the month.
He said: "I'm very excited to be joining Arsenal. They are one of the biggest teams in Europe with many great players. I'm really looking forward to playing in the English Premier League and the Champions League with my new club. Also, in Arsene Wenger, Arsenal have one of the best managers in the world and I can't wait to work with him and do my best for the Arsenal supporters."
Wenger had tracked the 24-year-old for some time as Koscielny, who is also eligible to play for Poland, impressed in the French domestic league.
The Gunners boss was in need of cover at the back, with Sol Campbell mulling over a new one-year deal and fellow veterans William Gallas and Mikael Silvestre set to leave after the end of their contracts.
Wenger has already secured the capture of long-term target Marouane Chamakh, the Morocco striker, to bolster the Arsenal attack, which could be missing Nicklas Bendtner ahead of their opening game of the new Barclays Premier League season at Liverpool on August 15.
Fulham's Australia international Mark Schwarzer has also been linked with a switch to the Emirates Stadium should Wenger decide he needs a more reliable pair of hands in goal next season.
The Gunners boss has been in South Africa working as a pundit for French TV, but the future of midfielder Cesc Fabregas, who is wanted by Barcelona, will be at the forefront of his mind when he returns.
The squad is set to head out to their Austrian training base before the Emirates Cup and by then Wenger will want the Spaniard's future sorted out one one way or another. Barcelona appear to be growing impatient in the pursuit of their former trainee, who new president Sandro Rosell maintains will not come at any cost.
Rosell is due to travel to South Africa shortly, where he hopes to meet with Wenger, and wants the issue sorted as soon as possible.
"It's now or never," he said in an interview with Sport. "We will do it fast. It won't be protracted.
"I'll try to see Wenger in South Africa, then we'll tell you what happens.
"We would not pay the 50-60million euros that I have read about.
"If Arsenal do not go crazy, he might play at Barca."
Lorient have moved quickly to fill the gap left by Koscielny's departure, with the signing of 21-year-old Gabon international Bruno Ecuele Manga from newly-promoted Angers.
"The timing is perfect. The arrival of Bruno is not a coincidence," said Lorient boss Christian Gourcuff.
"We have been following him for two years and when it became known that Arsenal were interested in Laurent, we became active."