The Ivory Coast international helped the Stade Lille-Metropole clinch the Ligue 1 and French Cup double last season, scoring 18 goals in 49 appearances in all competitions.
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"Gervinho is a player that can play in a number of positions up front. He can play on the right, on the left and through the middle," Arsenal boss Arsene Wenger told the club's official website.
"He has qualities that I find very important, like his movement off the ball. He has the qualities we like technically.
"He is good one against one, he is strong and was the best provider in the French league with assists and he scored 15 goals
"I think he is a very good addition to the squad."
The Ivory Coast international, who has won 27 caps for the Elephants, has long been linked with a move to the Gunners, with their North London rivals Tottenham Hotspur also rumoured to be interested in signing him.
However, the former Beveren and Le Mans man made no secret of his desire to seal a switch to Emirates Stadium, and revealed that he was fulfilling a dream by putting pen to paper with the Gunners.
"It's a great feeling to be an Arsenal player. I'm very happy. I've always dreamed to play for this club," he told the club's official website.
"I've achieved this dream now and I am so happy. It's one of the most beautiful days of my life. I'm very happy to have the chance to work with Arsene Wenger.
"I came here because I believe that he can improve my game and help me reach another level, but the most important thing for me is that I bring a lot to the team for whom I'm playing."
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