A case taken against the Data Protection Commissioner by an Austrian law student has begun in the High Court.
Max Schrems is seeking a judicial review after a complaint he made against Facebook was dismissed by the Data Protection Commissioner.
Mr Schrems had asked Billy Hawkes to investigate Facebook's transfer of its users' information from Europe to the United States.
He asked that claims by former US intelligence analyst Edward Snowden regarding Facebook be investigated.
Mr Snowden claims that private users' information is being used in the US National Security Agency's PRISM programme.
Mr Hawkes found that Facebook had no case to answer and that it was in compliance with the relevant regulations.
The commissioner plays a key role in the regulation of Facebook and other social media operations that have their European headquarters in Dublin.