Here is a round-up of reaction to the Ian Paisley announcement.
PRIME MINISTER GORDON BROWN
Ian Paisley has made a huge contribution to political life in Northern Ireland and the United Kingdom.
The whole country values and admires the manner in which he has led as first minister.
His commitment and dedication to public service deserve our gratitude. Progress on bringing a lasting peace to Northern Ireland would not have been possible without his immense courage and leadership.
IRISH PRIME MINISTER BERTIE AHERN
I honestly believe that it (devolution) will last because I believe there are very pragmatic people in all of the parties.
We hope and pray that what has been achieved through the leadership of Dr Paisley, and others, will continue.
TONY BLAIR, FORMER PRIME MINISTER
Ian Paisley's contribution to peace, after all the years of division and difference was decisive and determinative.
In short, in the final analysis, he made it happen. The man famous for saying 'no' will go down in history for saying 'yes'.
He did so personally convinced it was right and in reaching that conviction, consigning to the past the feelings he once so trenchantly articulated.
NORTHERN IRELAND DEPUTY FIRST MINISTER MARTIN MCGUINNESS
Ian Paisley has played a very powerful role in the course of the politics of the north of Ireland and the island of Ireland.
The historic decision he took to go into government with Sinn Fein has changed the face of Irish politics forever. I think that he will be fondly remembered by the people of Ireland - north and south - for the very courageous leadership that he showed.
IAN PAISLEY JNR, DEMOCRATIC UNIONIST PARTY
Ian Paisley is the epitome of a great Ulsterman. Like an anvil of old, hammer blows smash on him but he remains sure and unbowed.
To this son he is a great father. Indeed, everything a father could be.
My tribute to him cannot be measured in the tape of words but in the silence of an ever-thankful heart, a bottomless cavern of gratitude, love, devotion and regard will forever echo his praises.
PETER ROBINSON, DEMOCRATIC UNIONIST PARTY DEPUTY LEADER
It has been said that the greatest test of a politician's success is the degree to which he forces his opponents to change. By that standard, Ian Paisley's career has been a remarkable and outstanding success.
When Dr Paisley entered politics our position within the union was being eroded. Sinn Fein vowed to bring down Stormont. Today they are sitting inside Stormont in a Northern Ireland assembly as a minority party of a unionist majority executive.
The IRA was armed and engaged in a bloody murder campaign. Today republicans have been forced to give up their guns and embrace the policing structures of the British state.
DANNY KENNEDY, ULSTER UNIONIST PARTY DEPUTY LEADER
The attacks on Ian Paisley Jnr were used as proxy attacks on Ian Paisley Snr and were aimed deliberately at weakening his overall political position.
I think the party had come to the conclusion that the chuckle brothers issue was hurting them.
Baroness Paisley, earlier this week, was keen to stress that she believed that her husband still had work to do. That hasn't been the view that has prevailed in the assembly party or indeed other assembly colleagues.
MARK DURKAN, SDLP LEADER
While this is very significant political news, there is responsibility on all of us as politicians to make the most of the political processes here no matter who comes or goes.
In particular, we have to make a success of the investment conference in May and not allow this story to distort or distract from this focus
GRAND ORANGE LODGE
Ian Paisley has strode across the British and Irish political scene like a giant for many years.
No-one could ignore his forthright views and while not everyone agreed with him, his personal commitment was never in doubt.
He has been particularly supportive of the institution during the current campaign of arson attacks on Orange halls. We wish Dr Paisley a long and happy retirement.
JIM ALLISTER, TRADITIONAL UNIONIST VOICE LEADER
It has been quite clear for some time that Ian Paisley was going to be hung out to dry by the DUP pragmatists.
He had served his purpose. He had delivered what they had devised, but couldn't sell themselves - government with unrepentant terrorists.
SHAUN WOODWARD, NORTHERN IRELAND SECRETARY OF STATE
Dr Paisley has provided outstanding leadership as first minister and has brought his party to the historic position of power sharing government in Northern Ireland.
The establishment of peace and continued prosperity which everyone in Northern ireland now enjoys undoubtedly owes a significant debt to the leadership of Dr Paisley.
DAVID CAMERON, CONSERVATIVE PARTY LEADER
Ian Paisley has been a formidable figure in British politics for many decades.
His term as first minister of Northern Ireland has helped to forge a peace which many thought was impossible to achieve.
Dr Paisley's willingness to work closely with former opponents to build a new future for Northern Ireland has captured the world's imagination and earned him the gratitude of the people of Northern Ireland.
PETER HAIN, FORMER NORTHERN IRELAND SECRETARY OF STATE
He played an absolutely historic role in ending the deadlock and establishing permanent devolved government and deserves enormous credit for the courage and vision he showed.
I am sure that the decision he has taken will be the best one for his family as a very close family man. I wish him all the best for the future.
DAVID FORD, ALLIANCE LEADER
History will judge whether Ian Paisley will be remembered for 40 years of saying no or one year of saying probably.
Many will say his road to Damascus conversion came 35 years too late. The achievements of the executive since last May have been modest in the extreme.
PAULA DOBRIANSKY, US PRESIDENT'S SPECIAL ENVOY ON NORTHERN IRELAND
On behalf of the United States, I would like to congratulate Dr Ian Paisley on his service to the people of Northern Ireland, and his historic role in bringing about a peaceful political settlement that will ensure a better future for Northern Ireland.
I have been impressed by Dr Paisley's commitment to working for the greater good of the people of Northern Ireland in cooperation with Deputy First Minister Martin McGuinness and the Northern Ireland Executive. It has been my pleasure to work with him.