The State's appeal in the Apple ruling will be heard by Europe's second highest court in Luxembourg later today in what's being described as the world's biggest tax case.
It's after Ireland was ordered to recover €13 billion in back taxes and interest by the European Commission.
In 2016, the Commission found that Ireland "granted illegal tax benefits to Apple, which enabled it to pay substantially less tax than other businesses over many years".
Apple, along with the Irish State, have always fought against the Commission's decision.
While Ireland has collected the billions of euro from the tech giant, the money is being held in an escrow holding account until the appeals process has ended.
The case is now due before the EU's General Court.
Lawyers for Ireland will argue the State does not treat one company different to another.
They're alleging that the Commission made "manifest errors" in both its state aid assessment and understanding of Irish tax law.
Luxembourg is supporting Ireland in the appeal, while Poland is supporting the European Commission.
It will be up to the court to decide whether the Commission was right to place the record tax bill on the tech giant.