Senator George Mitchell, the US diplomat who chaired the negotiations, insisted there was much to celebrate despite the current political impasse at Stormont.
"Northern Ireland is a much safer, much better, much more successful place than it was 20 years ago," he said.
"The agreement did not purport to be the solution to all the problems for all time in Northern Ireland."
He said the problems facing devolution could be resolved.
"New challenges emerge," he said.
"I believe that this challenge can be met, as were the challenges of 1998, through courageous political leadership."
Northern Ireland has been without a functioning government since last January.
However, former Sinn Fein leader Gerry Adams has expressed confidence in the future.
He said: "The institutions will be back in place. The Good Friday Agreement remains the accord which is going to guide politics on this island and arrangements on this island and relationships on this island into the foreseeable future.
"I think the future is very bright. There is always an ebb in a process. There is always and ebb and a flow. We are in an ebb, it is temporary."