Willian has signed a new four-year deal at Chelsea, the club have confirmed.
Chelsea signed Willian from Shakhtar Donetsk on a five-year contract in 2013, quickly establishing himself as a key figure at Stamford Bridge.
The 27-year-old has now committed to the club until 2020, providing a boost for new coach Antonio Conte.
"I'm very happy to sign a new contract with Chelsea. It's a dream to continue with this club and over the next four years I will try to help the team win more trophies," said Willian.
"It's been an amazing time for me since I joined the club three years ago, I've won titles and last season I was named Chelsea Player of the Year.
"I hope to be able to stay at that level during the coming seasons and achieve more success."
Willian made 49 appearances in 2014-15 as Chelsea won a Premier League and League Cup double under Jose Mourinho.
However, a difficult campaign followed in which the club fell well short of mounting a serious defence of their title.
Willian's performances provided one of few positives in 2015-16, and the Brazilian was voted the club's Player of the Year by team-mates and fans.
Technical director Michael Emenalo added: "We are very pleased to agree a new long-term deal with Willian, who has proved himself to be an important player for the team since he arrived here.
"We are looking forward to seeing his continued impact as we begin an exciting new campaign under first-team head coach Antonio Conte."
