Havard Nordtveit has signed a five-year deal at West Ham on a free transfer deal.
The 25-year-old will join the Premier League side on 1st July when his contract with the Bundesliga side expires.
"It has always been a dream for me to play in the Premier League and now I have a big opportunity to do that for West Ham - I cannot wait to start!" Nordtveit told West Ham's official website.
"I came to Arsenal when I was 17 and from there I got a lot of first-team experience in training and friendlies. I sat on the bench in the Premier League, but never got a minute, so of course it is something I'm dreaming of.
"Now I'm back, I've had five-and-a-half years in the Bundesliga and hopefully that experience will help me to come into the game here.
"This team has something special, a spirit in the team that I can fit into. I will work hard and hopefully I can get some good moments at this club.
"I'm a player who can play many roles on the pitch, but I'm from Norway so maybe a little bit more running, tackles and try to spread a few balls around me.
"I'm looking forward to showing what I can do, but hopefully I have something to help West Ham achieve even more."
.@NFF_info star Havard Nordtveit will join West Ham on 1 July 2016 https://t.co/d30iVCc8Vj #HavardIsAHammer pic.twitter.com/ktiDF6uRL8
— West Ham United FC (@whufc_official) May 16, 2016