Curbishley took over from Alan Pardew in December 2006
Alan Curbishley has resigned as manager of West Ham because of a lack of control over transfer policy.
Curbishley tendered his resignation on Wednesday and it was accepted by owner Bjorgolfur Gudmundsson.
The final straw for the 50-year-old had been the enforced sales of Anton Ferdinand and George McCartney.
Curbishley said decisions had been made "without involving me", amounting to "a breach of trust and confidence meaning I had no option but to leave."
The former West Ham player, who succeeded Alan Pardew as manager at Upton Park in December 2006, added: "The selection of players is critical to the job of manager and I had an agreement with the club that I alone would determine the composition of the squad.
Curbishley quits as West Ham boss
"I started my West Ham career when I left school in 1974 and have remained a lifelong fan.
"I have been incredibly proud to manage such a great club and my decision to resign has been very tough.
"Nevertheless, I wish the club and the players every success in the future."
A West Ham statement said the club had accepted Curbishley's resignation "in the best interests of both parties".
It continued: "We wish Alan all the success in the future. A shortlist of candidates is being drawn up and an announcement will be made in due course about the new manager."
West Ham also moved to justify the summer departures of Ferdinand and McCartney to Sunderland, stating that the sales were "right for the club" and "based on our best long-term interests".
"In the past week, agreement could not be reached with Ferdinand on a new contract to replace his original deal that had just two years left to run," the club added.
"McCartney handed in a formal written transfer request after failing to resolve his personal reasons for wanting a move away."
When Curbishley took charge at Upton Park he was promised significant transfer funds to help achieve the objectives of a five-year plan, which would ultimately culminate in qualification for the Champions League.
He signed the likes of Kieron Dyer, Lucas Neill and Freddie Ljungberg during a summer of lavish spending in 2007 but his terms of reference changed this summer.
Gudmundsson told Curbishley he had to reduce the club's wage bill and that money was to be focused on training and medical facilities rather than signings.
Full-back Valon Behrami, who arrived from Lazio for £5m in July, was West Ham's only significant signing of the summer, while Jan Lastuvka, David Di Michele and Herita Ilunga joined on loan.
Yet first-team squad members John Pantsil, Bobby Zamora, Richard Wright, Ferdinand and McCartney all departed.
Technical director Gianluca Nani has been responsible for the club's transfer policy in conjunction with chief executive Scott Duxbury since being appointed in March.
This was clearly a major source of frustration to Curbishley and the League Manager's Association has complained about "the club's unilateral actions around player transfers, without reference to their manager".
Last May a senior boardroom member at West Ham explained to BBC Sport that the club's transfer policy was about to change.
"We have probably the biggest first-team squad in the Premier League and our transfer strategy has to be carefully planned going forward," he said.
"West Ham have a first-team squad of 40, so there is considerable room for manoeuvre. The last thing you should do when you have a problem is to throw money at it."
Curbishley oversaw a miraculous escape from relegation in the 2006/7 season, when Carlos Tevez scored the winner against Manchester United in their final league game.
The club finished 10th in the Premier League last season and are currently fifth in the table.
Former Hammers defender Slaven Bilic has been installed as the bookmakers' favourite to succeed Curbishley, with Harry Redknapp the second favourite.
While West Ham search for a new manager, reserve team boss Kevin Keen has been appointed caretaker manager.
West Ham's next manager will be their fifth in the seven years since Redknapp left in 2001, a stark contrast to the record of six managers in an 88-year period from 1902 to 1990.
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