Mourinho has left United on the back of a bruising 3-1 defeat at Liverpool
Manchester United have sacked manager Jose Mourinho after identifying a catalogue of his failings at the club.
The Portuguese, 55, took over in May 2016 and led United to League Cup and Europa League titles but they are 19 points behind league leaders Liverpool.
The club decided a change was needed after no progress with results or style despite spending £400m on 11 players.
The club also says the new manager will understand the philosophy of the club, including its attacking traditions.
It is understood that players and staff are not happy after a disappointing and unsettling period during which young players were not developed.
Manchester United are sixth in the Premier League, but closer to the relegation zone than leaders Liverpool, who beat them 3-1 on Sunday.
The decision to sack Mourinho, which will cost more than £18m, has been taken in the long-term interests of Manchester United with a regard that the club is bigger than any one individual.
Mourinho is understood to have wanted his own structure, but the new manager will be appointed with a head of football above him reporting to executive vice-chairman Ed Woodward.
A United statement said: "A caretaker-manager will be appointed until the end of the season while the club conducts a thorough recruitment process for a new, full-time manager.
"The club would like to thank Jose for his work during his time at Manchester United and to wish him success in the future."
The club hope to appoint a caretaker-manager before they face Cardiff City on 22 December but it will not be assistant manager Michael Carrick or academy boss Nicky Butt.
The candidate will be drawn from outside the club, but will not be former Arsenal boss Arsene Wenger.
Manchester United midfielder Paul Pogba posted a tweet saying 'caption this' before deleting the message soon afterA familiar conclusion to a rocky season
United's haul of 26 points after their first 17 Premier League games, is their worst tally in the top flight at this stage since 1990-91.
They are 11 points off the top four which would earn a Champions League qualification place.
Mourinho's sacking comes after a fall-out with £89m record signing Paul Pogba, who was an unused substitute for the defeat at Anfield on Sunday.
Following a 1-1 draw with Wolves, midfielder Pogba said he wanted United to be able to "attack, attack, attack" at home, which led Mourinho to say the France midfielder would no longer be the club's "second captain".
After Mourinho, who replaced Louis van Gaal in May 2016 and signed a contract extension in January, was sacked Pogba tweeted: "Caption this," with a knowing expression on his face, before deleting the social media post.
Former Manchester United defender Gary Neville replied: "You do one as well!"
In October, there were reports that Mourinho might be sacked prior to the home game against Newcastle, but after the team trailed 2-0, they turned it around to win 3-2 and seemingly buy the former Chelsea, Inter Milan and Real Madrid boss more time.
Mourinho's agent Jorge Mendes attempted to calm the storm earlier in December by taking the extraordinary step of issuing a statement to say Mourinho was "very happy" and "fully committed" to the club.
But despite reaching the Champions League last 16, where United will play Paris St-Germain, they have won just one of their past six games in the Premier League.
Mourinho's dismissal continues his run of never completing four consecutive seasons in charge of a club.
Only once has he made it into a fourth campaign, but he left Chelsea on 20 September 2007 during his first spell at Stamford Bridge.
Watch: Mourinho's last interview as Man Utd managerMourinho's record at United
Manager Games played Won Drawn Lost Goals for Goals against Win %
Jose Mourinho 144 84 32 28 243 117 58.33%
Alex Ferguson 1,500 895 338 267 2,769 1,365 59.67%
David Moyes 51 27 9 15 86 54 52.94%
Louis van Gaal 103 54 25 24 158 98 52.43%
The story of a chaotic season
29 July: Mourinho v pre-season tour - 'If I was the fans, I wouldn't come'
29 July: Mourinho v executive vice-chairman Ed Woodward - 'I gave the club a list of five names a few months ago'
10 August: Mourinho v Woodward part two - Manager's late attempts to sign defenders blocked
28 August: Mourinho v media - 'Respect, respect, respect'
1 September: Mourinho v Anthony Martial - Mourinho willing to let French forward leave
24 September: Mourinho v Pogba part one- Questions club tactics following 1-1 draw with Wolves
25 September: Mourinho v Pogba part two - 'No problems' but 'second captaincy' taken away
26 September: Mourinho v Pogba part three - Training-ground incident
1 October: Mourinho v the team - 'Some players care more than others'
20 October: Mourinho v Ianni - Touchline bust-up
7 November: Mourinho v Juventus fans - Did celebration go too far or show passion?
14 December: Mourinho v Man Utd team - Man Utd 'far' from being built in my image
16 December: Mourinho v Liverpool - Liverpool did everything better than us
18 December:Mourinho sacked
Other memorable Mourinho moments:
January 2017: Mourinho v fans - 'Don't come to the theatre'
April 2017: Mourinho v Luke Shaw - 'He is a long way behind'
March 2018: Mourinho v media - 12-minute speech on European record
Mourinho's United signings
Mourinho complained about the lack of new arrivals at Old Trafford, particularly in defence, during the summer.
During his time at Manchester United, he has signed 11 players for a total of £358.8m.
Player (in chronological order) Position Signed from Cost
Eric Bailly Centre-back Villarreal £30m
Zlatan Ibrahimovic Striker Paris St-Germain Free
Henrikh Mkhitaryan Midfielder Borussia Dortmund £26.3m
Paul Pogba Midfielder Juventus £89m
Victor Lindelof Centre-nack Benfica £31m
Romelu Lukaku Striker Everton £75m
Nemanja Matic Midfielder Chelsea £40m
Alexis Sanchez Forward Arsenal Swap involving Mkhitaryan
Diogo Dalot Full-back Porto £19m
Fred Midfielder Shakhtar Donetsk £47m
Lee Grant Goalkeeper Stoke £1.5m
Total - £358.8m
Source: bbc.com