Chelsea have announced the signing of defender Matt Miazga from New York Red Bulls on a four-and-a-half-year contract.
The 20-year-old arrives at Stamford Bridge having made 38 appearances for the Red Bulls, making his debut at the age of 18.
Miazga helped the MLS outfit to two Supporters' Shields as they topped the regular-season standings in 2013 and 2015.
The centre-back represents Chelsea's second new arrival in as many days, after Brazil international Alexandre Pato joined on loan from Corinthians until the end of the season.
Miazga told the Chelsea's official website: "I am very happy to sign for Chelsea, a world-famous club with a reputation for major success.
"I am delighted to be in the Premier League, the best league in the world, and can't wait to meet my team-mates and get going.
"I am still at the beginning of my career but I believe this is the place to develop and learn from some of the best players in the world."
Miazga's arrival follows the departure of Papy Djilobodji to Werder Bremen on loan, while doubt lingers over Gary Cahill's future at the club.
Having been faced with the decision of whether to represent Poland or the United States at senior international level, Miazga made his debut for the US against St Vincent and the Grenadines in November.