Striker Diego Costa has completed his move from La Liga champions Atletico Madrid to Chelsea after penning a five-year deal.
The 25-year-old told Chelsea's official website: "I am very happy to sign for Chelsea.
"Everybody knows it is a big club in a very competitive league, and I am very excited to get started in England with a fantastic coach and team-mates.
"Having played against Chelsea last season I know the high quality of the squad I am joining.
"I would like to thank everybody at Atletico who made me into the player I am, it was an incredible time for me, but now I am starting a new adventure and I hope to win many trophies with Chelsea."