Auxerre's Sagna signs for Arsenal
The 24-year-old, who was in the last France squad but is uncapped, has signed a long-term deal and said: "It is great to be joining Arsenal."
Gunners boss Arsene Wenger told the club's website: "He is a very capable defender and has played consistently well for Auxerre in recent seasons.
"He plays mainly at right-back, but can also play along the defence or in midfield. He is strong and quick."
Sagna, who will wear the number three shirt, has been a regular in the Auxerre team for the last three seasons and won the French Cup in 2005.
And Sagna added: "I know Abou Diaby from our time together at Auxerre and also Gael Clichy and Mathieu Flamini from the French Under-21 team.
"Also Arsene Wenger is a major reason why I have signed for Arsenal. He is an excellent manager with a fantastic record and I am really looking forward to working with him."