Crystal Palace have appointed former England boss Sam Allardyce as manager on a two-and-a-half-year deal, a day after sacking Alan Pardew.
Pardew was sacked on Thursday with the club 17th in the Premier League after a run of one win in 11 games.
Chairman Steve Parish said the club was "fortunate that someone of Sam's calibre and experience was available".
Allardyce has been out of work since losing the England job after 67 days, in the wake of a newspaper sting.
The 62-year-old will take training on Saturday, before Palace's Boxing Day game at Watford.
"You generally get a new job because there are difficulties at a club," Allardyce told Crystal Palace's website.
"I have to sort those difficulties out, hopefully with my experience, and try to get a few more results on the board, particularly over Christmas and New Year, to make everybody feel more comfortable."
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The former Bolton, Blackburn, Newcastle and West Ham boss saved Sunderland from relegation last season despite them being second from bottom when he joined.
After dismissing Pardew on Thursday, Parish said his "expansive style of football hasn't worked" and told BBC Sport the club would now "wind the dial back the other way".
Parish, who co-owns the club with American investors Josh Harris and David Blitzer, said relegation is "so costly" that a change was needed.
"The club itself seems to be very ambitious, certainly the chairman," said Allardyce. "The owners seem to taking the club forward in the right direction. I like the look of the squad.
"That's probably the reason that I am here because I feel that the club could go forward from here and, hopefully, I can help it go forward."
Caretaker manager Keith Millen took Friday's news conference and told the media that Allardyce would "sort the players out".
Pardew, 55, a former Palace player, was sacked after a miserable 2016 in which his side took just 26 points from the 36 Premier League matches they have played - and are only one point above the relegation zone.
The club's points-per-game tally of 0.72 in 2016 was their second worst in a calendar year - and their form for the year is the worst of all 92 Premier League and EFL clubs.
On 26 December 2015, Palace were fifth in the Premier League table. However, a 14-game winless run into April resulted in them finishing 15th.
Pardew led Palace to the FA Cup final for only the second time in their history, where they lost 2-1 to Manchester United at Wembley.
This season, the Eagles are the sixth highest scorers in the top flight but are third in the list of teams who have conceded the most goals.
"The strengthening in that [attacking] area by Alan and the club this summer has brought a lot of flair to the team and I think that has brought a few more goals," said Allardyce.
"But the other side is that when we aren't in possession we have just got to stop conceding goals and make sure the goals that we score win us games.
"It sounds simple but it's not that easy - that's what we have got to try to turn around."
With the January transfer window coming up, Allardyce is also planning to try to add "a little bit more strength in depth".
"The players here are good enough but, if we can add to that, let's try to do it," he added.
Allardyce and England
Allardyce left his post as England manager by mutual agreement in September after only one match in charge.
It followed a Daily Telegraph investigation claiming he offered advice on how to "get around" rules on player transfers.
The FA said Allardyce's conduct "was inappropriate". He did apologise but also said "entrapment had won".
Allardyce facts & figures
- Allardyce has never been relegated from the top flight as a manager and secured promotion to the Premier League with both Bolton and West Ham.
- Allardyce has a 33.6% Premier League career win percentage.
- Only Sir Alex Ferguson, Arsene Wenger, Harry Redknapp and his Sunderland successor David Moyes have managed more games in the top flight (467).
|Sam Allardyce's Premier League record|
What does Allardyce offer?
Allardyce is known for having an instant impact on sides when he joins them - shown below after he arrived at Blackburn Rovers (2008-09) and Sunderland (2015-16).
The graph also shows the dip in form immediately after Allardyce has left (Newcastle 2007-08) and Blackburn (2010-11).
Allardyce has become associated with a preference for direct football during his career.
As the graphs below show, during his season at Sunderland after joining in October 2015, they were among the most prolific long passers in the division and strong at set pieces.