Both men will be keen to fill the dangerous political vacuum left by Mr Blair's decision to postpone the Northern elections until the autumn.
Dissident republican's failed attempt to bomb the Belfast marathon yesterday will also focus both leaders' attention on getting the North's political institutions back on track.
"This meeting is not a cosmetic exercise to mend relations between Dublin and London following the Taoiseach's disapproval of the decision to postpone the Northern elections," a Department of Foreign Affairs spokesman said.
Mr Ahern wants to secure the policing and criminal justice reforms outlined in the Joint Declaration issued by both Governments and will want them implemented as soon as possible, the spokesman added.
Sinn Féin president Gerry Adams called on the Taoiseach yesterday to tell Mr Blair to hold the Northern Assembly elections as soon as possible.
But a Government spokesman said no comment was being made in advance of today's summit.
The Government's demands on the Joint Declaration were drawn up following a meeting between the Taoiseach, Foreign Affairs Minister Brian Cowen and Justice Minister Michael McDowell yesterday.
Criminal justice an independent oversight commission.
Police reform devolving full control to the North.
Equality and human rights proposals to go ahead.
The Taoiseach will not be able to press for the reduction of troops and the normalisation of military activities because the Joint Declaration states these will be conditional on the IRA conceding to end specified activities.
Mr Ahern will be pressing the British Prime Minister to implement the outstanding recommendations of the Patten Commission on policing and to put procedures in place for devolving control of the police service back to the North.
On criminal justice reform, the Taoiseach will be pressing for a new Criminal Justice Act that will bring in reforms demanded by nationalists and Dublin.
Mr Ahern will also be looking for a Criminal Justice Independent Oversight Commission to be set up, along with an Independent Judicial Appointments Commission and reform of the Director of Public Prosecutions office in the North.
"All these have been agreed in principle. It remains to be seen if we can get a set timeframe for their implementation," the Department of Foreign Affairs spokesman added.
Both Governments will also be keen to get pro-Agreement parties meeting again and will try to work out a timetable for this. Mr Blair is also expected to bring forward the autumn review of the Good Friday Agreement to the summer.