Monaco complete signing of Rennes' Bakayoko
The 19-year-old broke into the Rennes first team last season and was one of the bright spots in a disappointing season for the Breton club as they finished 12th in Ligue 1 and lost the Coupe de France final to local rivals Guingamp.
Bakayoko made 28 appearances in all competitions, scoring his only goal in a 5-0 win at Toulouse last October.
And the France Under-21 international will now look to continue his progression at the principality outfit.
"This is a first milestone in my career," Bakayoko told the club's official website.
"I am proud to sign for AS Monaco, a club that's on the up. I'm grateful to the club's board for showing faith in me."
Vice-president Vadim Vasilyev added: "We are delighted to be able to attract talented young French players with high potential like Tiemoue Bakayoko.
"He is part of our development and our strategy focused on building for the long term."