Taoiseach Bertie Ahern has led political tributes to outgoing Labour Party leader Pat Rabbitte, who announced his resignation this afternoon.
Mr Ahern said in a statement that Mr Rabbitte was "an able and talented political opponent".
"Pat Rabbitte's capacity and wit has enlivened politics and enlightened public debate over many years. Since he entered the Dáil in 1989 he has been one of the most eloquent and effective parliamentarians in the House," Mr Ahern said.
Green Party leader John Gormley
The Taoiseach said the Labour leader's genuine passion for his cause was married to "a forensic intelligence and considerable wit that made him a politician to be reckoned with, as well as parliamentarian who engaged the public's interest".
Green Party leader and Minister for the Environment John Gormley noted Mr Rabbitte's "committed and passionate leadership of the Labour Party".
"Pat Rabbitte showed great ambition for the Labour party and was an extremely competent and witty parliamentary performer. He managed to both entertain and enliven the Dáil over the last five years," he said.
"The Greens have enjoyed close cooperation with the Labour Party in opposition and regret that we have not yet had the opportunity to serve with them in government. I hope this possibility may arise in the future."
Fine Gael leader Enda Kenny also paid tribute to Mr Rabbitte, with whom he entered a pre-general election pact to form an alternative government to the outgoing coalition of Fianna Fáil and the Progressive Democrats.
"Today, Irish politics and society are the less for Pat Rabbitte's decision to resign as Labour leader. At a time when we need a better and broader vision for our country we have lost one of the few political leaders who espoused, passionately, such a vision," Mr Kenny said.
He said that working closely with Mr Rabbitte over the last five years had been "nothing short of an honour".
"Pat put patriotism over politics, he put the national interest over self-interest. He stood, literally, by the Republic, to make sure the electorate had a real choice at the last election."
Mr Kenny said that in every dealing, Mr Rabbitte proved himself to be a leader of the highest possible character, intelligence and integrity.
Sinn Féin Dáil leader Caoimhghín Ó Caoláin TD wished Mr Rabbitte well in his continued role as a member of the Dáil and said he hopes to have a good working relationship with whomever succeeds him as Labour Leader.
The Cavan-Monaghan TD said: "Though we have our political differences and have had an occasional spat on the floor of the Dáil chamber, I would like to wish Pat Rabbitte well in his continuing role as an elected member of the Dáil.
"While we will continue to have those differences we also share similar views, particularly on socio-economic issues, and our respective parties have supported each other when pressing those issues in the Dáil."
General secretary of the trade union Siptu, Joe O'Flynn, said Mr Rabbitte had championed a fairer society and, in particular, workers' rights.
"As a former industrial group secretary in the Irish Transport and General Workers' Union, which became one of the main constituent parts of SIPTU, Pat Rabbitte had an intimate knowledge of the world of work and how progressive political policies could advance the interests and standard of living for ordinary people," he said.
"On behalf of Siptu I would like to thank him for the tremendous work he did, particularly in defending vulnerable workers, especially migrants. He worked closely with us in disputes such as Gama and Irish Ferries, as well as in promoting stronger employment rights legislation, including the creation of the National Employment Rights Authority and the appointment of more labour inspectors."
Richard Boyd Barrett of the People Before Profit alliance said Mr Rabbitte's resignation was "a public admission that the party's political and electoral strategy has failed"
Mr Barrett, who unsuccessfully ran for the Dáil in Dun Laoghaire in May, said Labour had "disillusioned many of its natural political constituents of workers and trade union members, and spent the past fifteen years pursuing a strategy of accommodation with neo-liberalism".
"It has failed to confront the right-wing economic strategy of Fianna Fail and the PDs that puts the interests of wealthy and corporate Ireland before those of ordinary people."
He said Mr Rabbitte had "betrayed" not only the thousands who voted for Labour but also his own party members in his "unwillingness to tackle the government on the US military's use of Shannon airport".