The 29-year-old is keen to build on last season's loan at West Brom after securing a permanent switch to Upton Park for an undisclosed fee, the Hammer's ninth summer recruit.
The 29-year-old joins on a permanent deal after spending the 2013-14 season on loan at West Brom.
A versatile attacking midfield player, Amalfitano becomes Sam Allardyce’s ninth and final signing of the summer transfer window.
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"It's very good news and I'm very happy to come to this big club," the Frenchman told the Hammers’ official website. "I've waited a long time but I am very happy to have signed here. The club wanted me a lot and for that I waited for West Ham and now I'm here. The manager explained to me how the team plays and how he needs me. I explained to him where I prefer as my position in his team. This is a new team with very good players with great experience of this league. I think everything can go well and I hope we have a good season.
"I prefer to play behind the striker but last year, with West Brom, I played on the right. I like to cross the ball, too, but I can also give through passes from behind the striker. The coach will see what happens in every game and, if he finds another position for me in the team, there is no problem for me.
"I enjoyed my first year in English football and for that reason I have come back and hopefully I can improve again. The first year was good for my experience and I will try to help West Ham now by giving my best and continue to improve in this league. I like this country and this is the best league."