The head of the Revenue Commissioners has admitted it could be impossible to stop big companies from avoiding corporate tax.
Josephine Feehily says governments will never be able to predict how companies will avoid tax, and can only stop avoidance after it's already started.
She was speaking at the end of a major conference in Dublin where 38 governments discussed ways to clamp down on corporate tax avoidance.
Ms Feehily says they've done good work - but companies will always be one step ahead:
