Chelsea sign Borussia Dortmund forward for £58m
The twentty year old USA international, who was linked with Arsenal and Liverpool, joined Dortmund in 2015.
Pulisic has scored 9 goals in 23 games for the USA.
"It's a privilege to have signed for such a legendary club," he said.
It is the highest transfer fee for an American player, beating the 20 MLLION £ Wolfsburg paid for John Brooks in 2017.
Dortmund director Michael Zorc said: "It was always Christian's dream to play in the Premier League.
That certainly has to do with his American background, and as a result we were unable to extend his contract.
Against this background, we have decided to accept an extremely lucrative bid by Chelsea, given the low contract maturity.
Pulisic's contract at Dortmund was due to expire in June 2020.