Koscielny has yet to decide which country he will play for
Arsenal have bolstered their defence by signing centre-back Laurent Koscielny from Lorient for an undisclosed fee.
The 24-year-old Frenchman, who has signed a long-term contract, is also eligible to play for Poland.
"We identified him as a very strong centre-half, who has made big progress very quickly," said boss Arsene Wenger.
Koscielny improves Wenger's defensive options as Sol Campbell is mulling over a new one-year deal and William Gallas and Mikael Silvestre likely to leave.
Having sold Philippe Senderos to Fulham and with Gallas and Silvestre believed to have played their last games for the club after their contracts expired, Koscielny will provide Wenger with more defensive depth.
Media reports said the deal was worth £10m.
The central defender's move to the Emirates completes a remarkable rise for a footballer who was playing for Ligue 2 side Tours last year.
"Koscielny is a central defender with great ability who performed extremely well last season for Lorient," added Wenger.
"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 is Arsenal's second acquisition this summer, with Morocco striker Marouane Chamakh having joined from Bordeaux before the World Cup.
"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," said Koscielny, who will wear the number six shirt next season.
"It's true that it's a great league, physical. I'll have to adapt and give everything in training to get to the level for the Premier League.
"I have a certain apprehension. It's the start of a new adventure. I will give my maximum to play in the team."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.