Jake Livermore has joined Albion from Hull City for a fee believed to be around £10m.
The former England international midfielder has signed a four-and-a-half year contract and becomes Albion's first of the January transfer window.
Baggies boss Tony Pulis welcomed Livermore claiming he has been a long-time admirer of the 27-year-old.
“I watched him a lot when he was at Tottenham and thought he would go on to establish himself as a top six player.
“Maybe he has just drifted away a little from that – although having said that two promotions and a Cup final with Hull should not be forgotten. But I believe this lad is a very, very good player and I’m delighted we’ve got him.
“He is a fantastic character and as a player is good enough on the ball but also possesses fantastic energy. He’s a good age at 27 and I believe his next three or four years will be his best.
“There’s a dearth of mid-20s players in our group. We’ve got good young ones who are part and parcel of the future but we want to trim the age at the top end.
“At the same time, we need to get experienced players in – players who still have a lot left in the tank and something to prove and Jake is one of those players.”
Livermore joins from Hull City after make 25 appearances in all competitions this season for the Tigers. He joined City from Spurs for £8m in 2014 and went on to make more than 100 apperances in a Hull shirt.
He made his only appearace for England in a 2-1 friendly win against Italy in 2012.
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