Andre Schurrle will wear the No. 14 shirt at Chelsea next season after joining the club on Tuesday.
Schurrle completed his £18million move to Chelsea, signing a five-year contract with the Blues.
The 22-year-old scored 18 goals in 65 Bundesliga appearances for Bayer Leverkusen following his move from Mainz in 2011.
"I am so happy now I have signed and it is an honour for me to play for this club, with this team and for these great fans," said the Germany international, who has scored seven goals in 24 appearances for his country.
"I am really looking forward to it."
Schurrle is the first player to arrive at Stamford Bridge since Jose Mourinho's return to the club as manager.
Leverkusen had rejected a bid from Chelsea for Schurrle last summer.