Who needs to register?
Anyone who intends to work in Ireland, who is not a citizen of Ireland or the European Union/EEA.  EU/EEA citizens are not obliged to register, but may if they want to prove to their home country that they are non-resident there.

Nationals of non-EEA countries must register with the Garda Síochána (Police Force) in the areas in which they intend to reside within three months of arriving in the State (in Dublin this is the Immigration Office).  Holders of working visas and work authorisations must also arrange with the relevant previously-mentioned authorities to extend their permission to continue to reside in the State for the periods for which they are valid.