The Blues confirm that the Netherlands international midfielder, still only 20 years old, has signed a five-year contract at Stamford Bridge after leaving Vitesse.
The Netherlands international midfielder arrives in London to become Jose Mourinho's second signing after the capture of Andre Schurrle from Bayer Leverkusen.
The 20-year-old is delighted to have sealed his move, telling the club's official website: "I'm very happy to be here at such a nice club with great players. I am really happy, the stadium is good and the training ground is fantastic.
"I know about all the players and will meet them on Monday. I expect a lot, I've watched matches and it's really nice to be here."
Van Ginkel, who was named Dutch Talent of the Year last season, made his Netherlands debut in November and starred for the country's Under-21s in the European Championships in Israel this summer.