Dr Richard Haass has arrived for a crucial meeting with the five main parties at Stormont in an effort to conclude a deal to resolve outstanding controversial issues in the peace process.
On his way into the plenary session, accompanied by Prof Meaghan O'Sullivan, Dr Haass said: "We'll see how it goes, it's going to be an interesting evening."
It is hoped agreement can be reached on parading and a body to replace the Parades Commission, and on how to deal with the legacy of the Troubles.
However, hopes of an agreement on the highly divisive issue of flags and emblems appears to be further away and it could be left to a new commission to try to resolve those problems over the longer term
Earlier, Ulster Unionist leader Mike Nesbitt said he believed a positive outcome is possible if everyone shows the will to go for it.
He said the discussions would begin with a series of bi-lateral meetings with the other parties.
Gerry Kelly of Sinn Féin said the main issues were still about Britishness, Irishness and inclusivity.
DUP delegation leader Jeffrey Donaldson said that realistically it would be a challenge to produce an agreement on all the outstanding issues today.
Mr Haass, who is keen to secure a deal before Christmas, submitted a third draft set of proposals yesterday.
The third draft stated: "We could not reach a common position on the flying of flags".
It is thought a separate process will be recommended to try to resolve the contentious issue.
Dr Haass is due to return to the US tomorrow morning, but declined to comment on his way into the meeting when asked if he expected to make the flight.