An Bord Pleanála has begun a hearing into the controversial proposal to construct a new town the size of Drogheda at Lucan in Dublin.
Opponents have claimed Adamstown would create the largest traffic jam in the State.
However, planners have strongly defended the proposal as a forward-looking alternative to low-density suburban development.
The hearing, which is taking place in the Gresham Hotel, is expected to last more than a week.
Lucan is one of the fastest growing towns in Ireland. However, South Dublin County Council plans to build a new town close by to become home to up to 20,000 people.
Some residents in the west Dublin area have been incensed at the proposal, arguing that Lucan has one of the poorest public transport services of any urban area and there has been no environmental impact study conducted into Adamstown.
There were strong objections when the development came before the council earlier this year, and the decision to go ahead is now being appealed to An Bord Pleanála, which commences hearings today.
However, the scheme has been strongly defended by the council as a key development aimed at curbing the urban sprawl.
Planners argue that Adamstown will only be developed in stages to ensure they get it right and, while there has not been an environmental impact study, there has been a considerable appraisal and the original plan was amended.
Planners across the country will be watching the battle closely as Adamstown is the first such development to go through a fast track planning system.
