With discussion about the possible direction the DUP is going to take, Ulster Unionist leader Steve Aiken says his party would represent a "modern and progressive approach to unionism".
"It has to be more than anything else about good governance," he said.
BBCCopyright: BBC
"We need a period of stable and continuous government."
Mr Aiken said he had messaged Mrs Foster earlier on, and planned to speak to her soon.
He gave the outgoing DUP leader his best wishes, said she had shown "passion", and her resignation evidenced "how difficult the life of politics can be for people".
Poots thanks Foster for 'service, sacrifice and commitment'
DUP Agriculture Minister Edwin Poots tweets his best wishes "for whatever the future may hold" for Arlene Foster.
There is no future for unionism in division, Arlene Foster has said.
In a statement announcing her resignation, Mrs Foster said she had sought to lead Northern Ireland "towards a better path".
"There are people in Northern Ireland with a British identity, others are Irish, others are Northern Irish, others are a mixture of all three and some are new and emerging.
"The future of unionism and Northern Ireland will not be found in division, it will only be found in sharing this place we all are privileged to call home."
PacemakerCopyright: Pacemaker
Campbell praises Foster for 'faithful endeavours in all you tried to do'
DUP MP Gregory Campbell thanks Arlene Foster for her "faithful endeavours in all you tried to do".
In a Facebook post, he says his party leader "didn't shirk her responsibilities" as an assembly member or in her role as Northern Ireland's first minister.
In the wake of Arlene Foster's resignation, there are three potential candidates for leader, says our correspondent.
These are Gavin Robinson, Edwin Poots, and Sir Jeffrey Donaldson.
"Gavin Robinson, the East Belfast MP, young, moderniser, I would have said. Somebody close to Arlene Foster said he is more liberal than her," he told BBC's Evening Extra.
"On the other side of the party, from the traditional 'Paisley-ite' wing, you have Edwin Poots. He is not a one-dimensional character, he has served in government with Sinn Féin for a very long time.
"If anyone thinks they can categorise him easily, I think they are wrong.
"Those two candidates could lead the party in very different directions, and then someone who is in the middle is Sir Jeffrey Donaldson - he could be a bit of both."
"The DUP worry very much about haemorrhaging votes on one side to Alliance, on the other side to the TUV - and it is hard to ride both these horses.
"The DUP has got to decide in what direction it wants to go."
Foster 'broke a glass ceiling'
Don't let the lynch mob get you down - these are Arlene Foster's parting words to women in public office.
She said she had "broke a glass ceiling" with her election as DUP leader in 2015.
"I am glad I inspired other women to enter politics and spurred them on to take up elected office.
"I understand the misogynistic criticisms that female public figures have to take and sadly it’s the same for all women in public life.
"I want to encourage you to keep going and don’t let the online lynch mobs get you down."
PacemakerCopyright: Pacemaker
Empathy with Foster on personal level, says Stephen Farry
While his party has had issues with Arlene Foster's conduct as first minister, on a personal level "it is important to have empathy" with the departing DUP leader, Alliance MP Stephen Farry has said.
"This is not an easy thing to do in terms of announcing your resignation as party leader," he said.
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Mr Farry said Mrs Foster's leadership as first minister since 2016 had been "fairly disruptive"Image caption: Mr Farry said Mrs Foster's leadership as first minister since 2016 had been "fairly disruptive"
Mr Farry said he remembered Arlene Foster from before politics, and had been a student at the same time as her in Queen's University.
He said the "direction of travel" in Northern Ireland since the Brexit vote in 2016 had been "fairly disruptive" and this would not be missed as there was a "concern about what is coming next" in terms of the party's leadership.
'The political landscape across our island has changed' - O'Neill
Northern Ireland's deputy first minister says the incoming DUP leader "should recognise that the political landscape across our island has changed".
Michelle O'Neill says Arlene Foster informed her of her decision to step down earlier today.
"Throughout
the pandemic, I acknowledge the efforts Arlene Foster has made as first minister, and the service that she has given in working with the rest of the executive as we have battled the biggest health crisis in a generation," she says.
Mrs Foster is in a power-sharing role with Ms O'Neill, who is deputy leader of Sinn Féin.
Stormont uses a system of government known as power-sharing. This has allowed nationalist and unionist political parties to share power together in an executive (or government), alongside a legislative chamber made up of assembly members which proposes and scrutinises laws.
“As joint head of government, my
focus, and the focus of our executive, must remain on the task of leading us
safely and sustainably out of the pandemic, building a fairer economy recovery,
providing first-class public services and delivering the New Decade, New Approach deal to the benefit of every section of our society," said Ms O'Neill.
'It's been a privilege to work alongside you' - deputy leader Dodds
DUP deputy leader Nigel Dodds says Arlene Foster "has dedicated her life to defending the union and moving Northern Ireland forward".
He tweets that she "has demonstrated great courage and is an example for women in public life".
"It's been a privilege to work alongside you," he adds.
Rumours about bids to remove Arlene Foster from the helm of the Democratic Unionist Party had been swirling for months.
On many occasions they'd been easily shrugged off by the first minister.
But she could shrug no longer, given many of those previously loyal to her abandoned the Foster ship.
However, questions remain about the move's timing and what has caused it.
PA MediaCopyright: PA Media
Firstly, pressure to remove her has come from the outworkings of Brexit and the Irish Sea border.
Party sources have also given strong hints about growing concern that Mrs Foster held a softer stance on some social issues than her predecessors and was willing to move the party in that direction.
The DUP's roots are deeply conservative, staunchly opposing abortion and same-sex marriage.
In her statement, Arlene Foster said she was preparing to "depart the political stage".
Speaking of her time as first minister as "the privilege of my life", she said her decision to enter politics "was never about party or person".
She added: "It is my view that if Northern Ireland is to prosper then it will only do so built on the foundations of successful and durable devolution.
"That will require continued hard work and real determination and courage on all sides."
PacemakerCopyright: Pacemaker
From trailblazing leader to party civil war
From Brexit to the Irish Sea border, and of course the Covid-19 pandemic,
it has been a tough few years for Northern Ireland's first minister,
culminating in the revolt that has forced Arlene Foster to step down.
Born Arlene Kelly in 1970, she grew up on a farm in rural County Fermanagh, close to the Irish border.
After leaving the Ulster Unionist Party to join the Democratic Unionist Party in 2004, she went on to hold ministerial posts before her election as DUP leader in 2015.
PacemakerCopyright: Pacemaker
BBC News NI has charted Mrs Foster's life and career, from County Fermanagh lawyer to Stormont's first minister.
Arlene Foster has gone from being a electoral asset to being pushed out by some of the MLAs she helped get elected, our Political Correspondent Enda McClafferty says.
"I would imagine behind the scenes there will be a process about who is going to replace Arlene Foster as party leader, " he told BBC Radio Ulster's Evening Extra programme.
"We know there are rules within the party about when that will take place, within the next seven days perhaps.
He said the party will now be examining a system of "having a party leader and first minister in Belfast".
On the response of Sinn Féin, he said the party had expressed its feelings that the situation should not "get in the way of good governance” in the Executive.
"I think Sinn Féin and others will be sitting back and waiting to see how this plays out."
'I will work with the new leader'
Arlene Foster has vowed to work with the new leader of the DUP.
In a statement, she said would give party officers the space to arrange an election for a new leader.
She will step down from the leadership on 28 May, and as first minister at the end of June.
ReutersCopyright: Reuters
She said: "As first minister it is important that I complete work on a number of important issues for Northern Ireland alongside other Executive colleagues.
"Northern Ireland and its people have been heavily impacted by the Covid-19 pandemic and there remains more work to be done to steer us thorough the pandemic and to lessen its impact on the lives of everyone."
Arlene Foster to resign as first minister and DUP leader
PacemakerCopyright: Pacemaker
Arlene Foster at the 2016 Assembly electionImage caption: Arlene Foster at the 2016 Assembly election
Hello and welcome to our live coverage as Arlene Foster announces her resignation as leader of the Democratic Unionist Party (DUP) and as Northern Ireland's first minister after an internal revolt.
We'll have all the reaction throughout the evening. Do stay with us.
Live Reporting
All times stated are UK
'Modern and progressive unionism needed'
With discussion about the possible direction the DUP is going to take, Ulster Unionist leader Steve Aiken says his party would represent a "modern and progressive approach to unionism".
"It has to be more than anything else about good governance," he said.
"We need a period of stable and continuous government."
Mr Aiken said he had messaged Mrs Foster earlier on, and planned to speak to her soon.
He gave the outgoing DUP leader his best wishes, said she had shown "passion", and her resignation evidenced "how difficult the life of politics can be for people".
Poots thanks Foster for 'service, sacrifice and commitment'
DUP Agriculture Minister Edwin Poots tweets his best wishes "for whatever the future may hold" for Arlene Foster.
Foster key to powersharing return - former NI secretary
Former NI Secretary of State Julian Smith pays tribute to Arlene Foster, saying she was "key to getting powersharing returned".
Foster will have 'inspired' many young women
Northern Ireland Secretary Brandon Lewis describes Arlene Foster as "a truly dedicated public servant".
He tweets that many people will be inspired by her example to follow a path into politics.
No future for unionism in division, says Foster
There is no future for unionism in division, Arlene Foster has said.
In a statement announcing her resignation, Mrs Foster said she had sought to lead Northern Ireland "towards a better path".
"There are people in Northern Ireland with a British identity, others are Irish, others are Northern Irish, others are a mixture of all three and some are new and emerging.
"The future of unionism and Northern Ireland will not be found in division, it will only be found in sharing this place we all are privileged to call home."
Campbell praises Foster for 'faithful endeavours in all you tried to do'
DUP MP Gregory Campbell thanks Arlene Foster for her "faithful endeavours in all you tried to do".
In a Facebook post, he says his party leader "didn't shirk her responsibilities" as an assembly member or in her role as Northern Ireland's first minister.
Three main contenders for leadership
Gareth Gordon
BBC News NI Political Correspondent
In the wake of Arlene Foster's resignation, there are three potential candidates for leader, says our correspondent.
These are Gavin Robinson, Edwin Poots, and Sir Jeffrey Donaldson.
"Gavin Robinson, the East Belfast MP, young, moderniser, I would have said. Somebody close to Arlene Foster said he is more liberal than her," he told BBC's Evening Extra.
"On the other side of the party, from the traditional 'Paisley-ite' wing, you have Edwin Poots. He is not a one-dimensional character, he has served in government with Sinn Féin for a very long time.
"If anyone thinks they can categorise him easily, I think they are wrong.
"Those two candidates could lead the party in very different directions, and then someone who is in the middle is Sir Jeffrey Donaldson - he could be a bit of both."
"The DUP worry very much about haemorrhaging votes on one side to Alliance, on the other side to the TUV - and it is hard to ride both these horses.
"The DUP has got to decide in what direction it wants to go."
Foster 'broke a glass ceiling'
Don't let the lynch mob get you down - these are Arlene Foster's parting words to women in public office.
She said she had "broke a glass ceiling" with her election as DUP leader in 2015.
"I am glad I inspired other women to enter politics and spurred them on to take up elected office.
"I understand the misogynistic criticisms that female public figures have to take and sadly it’s the same for all women in public life.
"I want to encourage you to keep going and don’t let the online lynch mobs get you down."
Empathy with Foster on personal level, says Stephen Farry
While his party has had issues with Arlene Foster's conduct as first minister, on a personal level "it is important to have empathy" with the departing DUP leader, Alliance MP Stephen Farry has said.
"This is not an easy thing to do in terms of announcing your resignation as party leader," he said.
Mr Farry said he remembered Arlene Foster from before politics, and had been a student at the same time as her in Queen's University.
He said the "direction of travel" in Northern Ireland since the Brexit vote in 2016 had been "fairly disruptive" and this would not be missed as there was a "concern about what is coming next" in terms of the party's leadership.
'The political landscape across our island has changed' - O'Neill
Northern Ireland's deputy first minister says the incoming DUP leader "should recognise that the political landscape across our island has changed".
Michelle O'Neill says Arlene Foster informed her of her decision to step down earlier today.
"Throughout the pandemic, I acknowledge the efforts Arlene Foster has made as first minister, and the service that she has given in working with the rest of the executive as we have battled the biggest health crisis in a generation," she says.
Mrs Foster is in a power-sharing role with Ms O'Neill, who is deputy leader of Sinn Féin.
Stormont uses a system of government known as power-sharing. This has allowed nationalist and unionist political parties to share power together in an executive (or government), alongside a legislative chamber made up of assembly members which proposes and scrutinises laws.
“As joint head of government, my focus, and the focus of our executive, must remain on the task of leading us safely and sustainably out of the pandemic, building a fairer economy recovery, providing first-class public services and delivering the New Decade, New Approach deal to the benefit of every section of our society," said Ms O'Neill.
'It's been a privilege to work alongside you' - deputy leader Dodds
DUP deputy leader Nigel Dodds says Arlene Foster "has dedicated her life to defending the union and moving Northern Ireland forward".
He tweets that she "has demonstrated great courage and is an example for women in public life".
"It's been a privilege to work alongside you," he adds.
Foster faced 'difficulties with courage and determination' - Robinson
DUP MP for East Belfast Gavin Robinson tweets his thanks to his party leader.
He describes Arlene Foster as "a constant source of encouragement to me and my colleagues throughout the province".
Mr Robinson adds that she has faced "difficulties with courage and determination".
Education minister 'sorry' to see Foster step down
DUP Education Minister Peter Weir says he is "sorry" to see Arlene Foster step down as party leader.
"I have known her and been a friend and colleague for over 30 years," he tweets.
Why did the DUP move against its leader?
Jayne McCormack
BBC News NI political reporter
Rumours about bids to remove Arlene Foster from the helm of the Democratic Unionist Party had been swirling for months.
On many occasions they'd been easily shrugged off by the first minister.
But she could shrug no longer, given many of those previously loyal to her abandoned the Foster ship.
However, questions remain about the move's timing and what has caused it.
Firstly, pressure to remove her has come from the outworkings of Brexit and the Irish Sea border.
Party sources have also given strong hints about growing concern that Mrs Foster held a softer stance on some social issues than her predecessors and was willing to move the party in that direction.
The DUP's roots are deeply conservative, staunchly opposing abortion and same-sex marriage.
Read more from Jayne here.
Foster prepares to 'depart political stage'
In her statement, Arlene Foster said she was preparing to "depart the political stage".
Speaking of her time as first minister as "the privilege of my life", she said her decision to enter politics "was never about party or person".
She added: "It is my view that if Northern Ireland is to prosper then it will only do so built on the foundations of successful and durable devolution.
"That will require continued hard work and real determination and courage on all sides."
From trailblazing leader to party civil war
From Brexit to the Irish Sea border, and of course the Covid-19 pandemic, it has been a tough few years for Northern Ireland's first minister, culminating in the revolt that has forced Arlene Foster to step down.
Born Arlene Kelly in 1970, she grew up on a farm in rural County Fermanagh, close to the Irish border.
After leaving the Ulster Unionist Party to join the Democratic Unionist Party in 2004, she went on to hold ministerial posts before her election as DUP leader in 2015.
BBC News NI has charted Mrs Foster's life and career, from County Fermanagh lawyer to Stormont's first minister.
Read more here.
'She has been pushed out'
Enda McClafferty
BBC News NI political editor
Arlene Foster has gone from being a electoral asset to being pushed out by some of the MLAs she helped get elected, our Political Correspondent Enda McClafferty says.
"I would imagine behind the scenes there will be a process about who is going to replace Arlene Foster as party leader, " he told BBC Radio Ulster's Evening Extra programme.
"We know there are rules within the party about when that will take place, within the next seven days perhaps.
He said the party will now be examining a system of "having a party leader and first minister in Belfast".
On the response of Sinn Féin, he said the party had expressed its feelings that the situation should not "get in the way of good governance” in the Executive.
"I think Sinn Féin and others will be sitting back and waiting to see how this plays out."
'I will work with the new leader'
Arlene Foster has vowed to work with the new leader of the DUP.
In a statement, she said would give party officers the space to arrange an election for a new leader.
She will step down from the leadership on 28 May, and as first minister at the end of June.
She said: "As first minister it is important that I complete work on a number of important issues for Northern Ireland alongside other Executive colleagues.
"Northern Ireland and its people have been heavily impacted by the Covid-19 pandemic and there remains more work to be done to steer us thorough the pandemic and to lessen its impact on the lives of everyone."
Arlene Foster to resign as first minister and DUP leader
Mrs Foster said she would step down as DUP leader on 28 May and as first minister at the end of June.
In a statement, Mrs Foster said it had been "the privilege of her life" to serve as first minister.
It comes as she was facing a revolt among her party's representatives.
Full story here.
Welcome
Hello and welcome to our live coverage as Arlene Foster announces her resignation as leader of the Democratic Unionist Party (DUP) and as Northern Ireland's first minister after an internal revolt.
We'll have all the reaction throughout the evening. Do stay with us.