President Mary McAleese has led tributes to Bertie Ahern following his announcement he would resign next month.
"Mr Ahern prepares to leave office, I would like to compliment him warmly on his achievements as Taoiseach," Mrs McAleese said. "His contributions to our thriving economy and to peace in Northern Ireland were hugely important and he deserves every credit for the work he has done," she added. "Bertie Ahern will be remembered as one of the outstanding politicians of his generation both nationally and internationally."
Tánaiste Brian Cowen said Mr Ahern's contribution to the creation of a "peaceful, successful, confident and modern Ireland" had been "incalculable".
Mr Cowen, who is widely expected to succeed Mr Ahern as Taoiseach and Fianna Fail leader, said that in coming to his decision, the Taoiseach had "once again put the interests of the nation first".
He praised Mr Ahern’s political achievements, including his work on the peace process in Northern Ireland and his stewardship of the presidency of the EU in 2004, when 10 new member states were admitted to the union. Mr Cowen also noted Mr Ahern’s forthcoming address to the US joint Houses of Congress on April 30th, which he said was an "extraordinary honour rarely bestowed".
"He has enhanced Ireland’s standing in the world," Mr Cowen said.
"I want to thank him for his comradeship his courtesy and his commitment to our political cause. Never have those traits been more in evidence than in the decision which he has announced today," Mr Cowen said.
"Bertie Ahern’s contribution to the creation of today’s peaceful, successful, confident and modern Ireland has been incalculable.
"From when he first entered government he has served Ireland’s interests with a commitment and drive unequalled by anyone of his political generation. His enthusiasm and energy levels never dimmed. He has played the major role in charting an economic, social and political course for this island during his tenure as Taoiseach."
"His application, his political judgement, his determination and his conciliatory manner are among the special characteristics that helped him to shape the Ireland we live in today. And I expect that, in time, those attributes will find a new home where they will have the same powerful impact they have had in his life’s work to date."
The Tanaiste expressed his appreciation for the opportunities the Taoiseach had given him to serve in government over the last 11 years.
"Political life is challenging. It has become more so during my time in Dail Éireann and to have worked closely with someone of Bertie Ahern’s particular talents has been a most valuable experience. It has been a privilege to serve under him."
Progressive Democrat leader and coalition partner Mary Harney said the Taoiseach, his family and friends could be very proud of his service to his country.
“His political skill, dedication and hard work as Taoiseach has delivered historic, permanent political agreement and peace on the island of Ireland; 11 years of stable, partnership, coalition government; an unsurpassed economic performance; and a higher standing for Ireland in the EU and internationally,” the Health Minister said.
“These are permanent, lasting achievements and will be Bertie Ahern’s undiminished legacy,” she added.
Minister for Justice Brian Lenihan said he was "surprised" at Mr Ahern’s decision, but said he was "proud" to have worked with him. He only learned of Mr Ahern's intentions this morning.
Former minister for finance Charlie McCreevy said he had known Mr Ahern for over thirty years as "a loyal friend, a tireless TD and community worker, a brilliant organiser and conciliator, and at government level as an outstanding negotiator, healer and tactician".
"His even temperament and masterly inter-personal skills were such that despite all the years working with him as Minister for Finance - and our somewhat divergent political philosophies - we never once fell out.
"For him that is a real tribute. For me it is a lifetime record.
Nothing must be allowed to detract – now or in the future - from the rightful recognition of the scale and scope of his contribution to so many dimensions of Irish public life over so long, to his dedication to his constituents and to his commitment to the public good. In all of these respects Bertie Ahern has no peer."