Maurizio Sarri says he wants to bring "entertaining football" to Chelsea after becoming their manager on a three-year deal.
The 59-year-old replaces fellow Italian Antonio Conte, who was sacked on Friday after two years at Stamford Bridge.
Sarri led Napoli to two second-place finishes in his three seasons in charge of the Serie A side, who named Carlo Ancelotti as his successor in May.
"It is an exciting new period in my career," said Sarri.
"I hope we can provide some entertaining football for our fans and that we will be competing for trophies at the end of the season, which is what this club deserves."
He is the 13th managerial appointment by Blues owner Roman Abramovich since his takeover of the club in 2003, including Jose Mourinho and Guus Hiddink on two occasions.
Sarri's appointment had been widely expected, with Chelsea agreeing compensation to bring him to Stamford Bridge because he had two years left on his Napoli deal and had remained on the Italian club's payroll after Ancelotti's arrival.