Manuel Lanzini has signed a new long-term contract with West Ham.
The new deal keeps the 26-year-old at the club until 2023 with the option of a further two years.
"I'm so happy to sign a new contract for West Ham," Lanzini told the club's website.
"I think it's the best decision for me. I've been here for a long time and I've said in an interview before that I like West Ham, I like the fans, I like the staff and when I came here all the people were comfortable with me. I like to stay here.
"It's a big decision but also easy, because when you feel good in one club and you like the club and the club likes you, it's easier to decide these things. For me, it was not difficult. It was easy, because I love it here.
"I love London, I love the club, I am happy here, we have a very good team, we have a very good manager and the club wants to change and to be in more competitions in the future and that's good for us."
The Argentina international joined West Ham from Abu Dhabi side Al-Jazira for £9.4m in 2015 and recently made his 100th Premier League appearance, scoring 20 goals.
How has Lanzini fared so far this season?
Following a full pre-season, Lanzini appears to have returned to the form he showed prior to his devastating knee injury.
He was West Ham's best player during pre-season and showed his ability to add goals from midfield, scoring in three successive friendlies against Fulham, Hertha Berlin and Athletic Bilbao.
Lanzini has continued that form into the new season and was a standout performer in the 1-1 draw at Brighton earlier this month, providing the assist for Javier Hernandez to open the scoring at the Amex Stadium.
West Ham beat Watford 3-1 at Vicarage Road on Saturday to secure their first win of the season, with Lanzini once again influential. He showed composure and quick feet in the penalty area to win a spot-kick in the second minute of the match, which captain Mark Noble converted.
Lanzini remained a constant thorn in the Watford defence and provided the corner that led to Sebastien Haller's second goal of the game.
Why do West Ham need him to stay?
Manager Manuel Pellegrini, director of football Mario Husillos and co-owner David Sullivan have built a squad with an abundance of attacking talent.
Lanzini - nicknamed 'The Jewel' - is a key component of West Ham's creative options and has consistently shown his ability to be the man relied upon.
His ability to collect the ball from deep, drive forward and create scoring opportunities for his team-mates is invaluable to the way Pellegrini wants to play.
He has shown himself an able finisher in front of goal and has the pedigree to capitalise on dead-ball situations.
Lanzini is arguably entering the peak years of his career and, as he showed against Brighton and Watford, appears ready to take on the role of talisman at West Ham.
How significant will this be for West Ham?
West Ham are keen to retain their very best talent and the contract extension for Lanzini will send out a signal of intent from the club.
In recent years, they have had to deal with the problematic sales of Dimitri Payet and Marko Arnautovic, which affected the playing squad and did not represent a great financial return for the club.
Pellegrini now has a settled squad to choose from and retaining Lanzini will only help boost his aim of securing European football this season.
Prior to his injury, Lanzini had been linked with a move away from the club with Liverpool mooted as a potential suitor for him.
But, with a new contract likely to see Lanzini spend the best years of his career with the club, West Ham will hope any suggestion of them being a selling club will have reduced significantly.