The Netherlands international is Pep Guardiola’s fourth summer signing with Rayan Ait-Nouri, Marcus Bettinelli and Rayan Cherki having also joined.
Reijnders, 26, was signed in time to be eligible for this month’s Club World Cup in America and could make his debut on 18 June against Wydad FC.
“I am ecstatic to be signing for Manchester City,” Reijnders said. “City are one of the biggest teams in the world, with the best coach, world-class players and outstanding facilities.
“Under Pep Guardiola, City have won so many titles and I want to help keep that going with a lot more success in the coming years.”
The midfielder has been capped 23 times by the Netherlands but was left on the bench during Tuesday night’s 8-0 thrashing of Malta.
He scored 15 goals in 54 matches across all competitions for Milan last term and was named Serie A’s midfielder of the season.
With Kevin de Bruyne departing the club, Reijnders will strengthen the centre of the pitch for Guardiola as they look to improve on their third-placed Premier League finish last season.
A question being asked in the lead up to the Club World Cup was how seriously teams would be taking the expanded competition.
Manchester City have emphatically answered that question by moving quickly to bolster a wounded squad that will now hope to go far in the competition in the United States.
With De Bruyne departing and a hole left in attacking midfield, City were eyeing up Bayer Leverkusen’s Florian Wirtz but decided not to pursue a deal.
Instead, they have boosted the side with the signings of midfielder Reijnders and Cherki and left-back Ait-Nouri for a total of around £108m, which is less than the reported 150m Euros (£127m) asking price for the Germany international.
All three, plus new goalkeeper Bettinelli, are available for selection for the Club World Cup with City facing Moroccan side Wydad AC in Philadelphia first on 18 June.
Reijnders joins City in a period which feels like a revolution rather than a renewal, and one that may require a revolving door at the Etihad over the next few months.
Attacking midfielder Cherki has already joined, while midfielders Kalvin Phillips, James McAtee and Jack Grealish have all been tipped to leave the club, along with defender Kyle Walker who spent the latter part of last season out on loan.
The squad also includes Ederson, Stefan Ortega, Nathan Ake and John Stones, whose futures have also been the topic of much media speculation.
Finding the right time to replace ageing stars like Ilkay Gundogan, Bernardo Silva and the injured Mateo Kovacic in City’s midfield will also surely be in Guardiola’s thinking.
Despite the £50m acquisition of Nico Gonzalez in February, the lack of running power and physicality in City’s engine room was exposed last season as they failed to win a major trophy for the first time in eight years.
Reijnders, who turns 27 in July, is viewed as the man to help alter that dynamic.
A powerful box-to-box midfielder, Reijnders ended last season with 10 goals and four assists in Serie A, with only one player in his position, Napoli’s Scott McTominay (16), having more goal involvements.
His performances were also considered one of the few positives in a disappointing season for Milan, who finished eighth in Serie A and missed out on European qualification.
Reijnders was ranked ninth for forward passes in Italy’s top flight last term and was fifth for through balls and carrying the ball.
He also ranked seventh overall for carries of more than 10m in Serie A last season but more significantly, Reijnders, who joined AC Milan for around £21m in 2023, is capable of doing so all over the pitch, an asset that could be crucial in Guardiola’s transitional play.
He excels at bringing out the best in attacking players around him: he was involved in an unrivalled 205 passages of play which ended in a shot being attempted in Serie A last season – the most of any player.
Reijnders also ranked second of all Serie A players for secondary chances created (49) – in other words, getting the right players into the best positions to create a chance for a team-mate.
“He will slot in very well at City, he runs a lot, he’s very willing to improve and he will love working with Guardiola,” said Italian football journalist Daniele Verri.
“He improved a lot since his first season at AC Milan.”
