The President, Mrs McAleese, said Mr John Hume's "contribution to political progress in Northern Ireland has been immeasurable, as has his role in the completion of the negotiations leading to the Good Friday agreement". He would continue to make an important contribution to progress through constitutional dialogue.
The Taoiseach described Mr Hume as a "true Irish hero" who had "served his people to the limits". Mr Hume had "laboured tirelessly" in the search for peace for over 30 years. Mr Ahern said he had learned of his decision to step down with a sense of sadness, but also immense gratitude for his magnificent public service.
Mr Ahern said when violence and hatred had threatened to overwhelm those seeking a political solution, the name of John Hume became synonymous with a refusal to yield to the forces of hatred.
"The philosopher, architect, and ultimately symbol of peace, John Hume never faltered in his insistence that dialogue was the only way forward, never tired in his efforts to persuade others to come around the table; never failed in his belief that a peaceful solution could be found to the problems on this island."
The Tanaiste, Ms Harney, said Mr Hume's decision to stand down marked the end of an era. He had proved to be the true leader of Irish nationalism, using only the power of his arguments to win people around to his point of view.
The Fine Gael leader, Mr Michael Noonan, said Mr Hume had made "an outstanding contribution to the building of relationships between the peoples of this island and the peoples of Britain, of Europe and of the United States".
The Labour Party leader, Mr Ruairi Quinn, said: "That we have come as far as we have in the peace process is a testament to the tenacity and the commitment of John Hume."
The former Taoiseach, Mr John Bruton, said Mr Hume's "genius lay in recasting the idea of national self-determination into a form that recognised the rights of unionists and the vital principle of consent".
The former Taoiseach, Dr Garret FitzGerald, said: "All of us owe him a huge debt for the way in which he led Northern nationalism away from the sterile anti-partitionism of earlier decades, withstood powerful sectarian pressures, and finally persuaded the leadership of Sinn Fein to abandon violence."