The 26-year-old midfielder has spent the last two seasons at the Nou Camp following his £15m move from Arsenal in the summer of 2012, playing 39 La Liga matches and winning the title in 2012-13.
I am very excited to be part of this project
The Cameroon international admits he is delighted to be back in the Premier League after his two-year spell in Spain, despite having offers from a number of clubs playing in the Champions League.
“I’m very happy to be here and very happy to see the guys and the fans today and to start to do my job for West Ham United,” Song said.
“I think this is very important for me to be coming back to London to West Ham United, which is a club with ambition to build a new stadium and become a big club. I am very excited to be part of this project.
“For me, when I was in Spain, I always said that if I was to leave one day I would return to the Premier League.
“It was a very hard decision, because when you have options of a lot of clubs who are playing in the Champions League, but at the end of the day I chose West Ham because I wanted to come to the Premier League.
“This is a league which has given me a lot and I didn’t finish what I wanted to achieve here.”
Song made 138 Premier League appearances for Arsenal – 206 in all competitions – and was a League Cup runner-up in 2011.
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