West Ham have completed the signing of Czech Republic midfielder Tomas Soucek from Slavia Prague.
Soucek, 24, has initially joined on loan, with West Ham holding an option to make the move permanent at the end of the season.
David Moyes' side confirmed the deal on Wednesday ahead of their home match with Premier League leaders Liverpool.
"We are delighted to welcome Tomas to West Ham United," Moyes said of Soucek, who has 25 international caps.
"He gives us a lot of different qualities, but most importantly he fits the profile of the player we want to bring to the club. He is young and hungry but with an established pedigree and proven talent."
Soucek has scored 12 goals this season, including strikes against Inter and Borussia Dortmund in the Champions League.
He netted on 18 occasions last season as he helped Slavia to a league and cup double on his way to being named the Czech top-flight's Player of the Year.
Moyes added: "He was captain of Slavia Prague, he's played as a defensive midfielder but he's scored a lot of goals as an attacking midfielder as well.
"At the moment he ticks a lot of boxes. We need to give him the opportunity and time to settle in but we are confident he will prove to be a strong addition to the squad."
Soucek is West Ham's second signing of the January transfer window after the addition of goalkeeper Darren Randolph.