Assuming interest from an EU source:
Taxation
EU deposit interest received by individuals who are liable to income tax in Ireland from banks, building societies, etc. in EU countries will be subject to tax at the same rate as deposit interest received by individuals from lending institutions in Ireland, currently 33%.
If you are a 'chargeable person' there will be 4% PRSI due in addition to tax @ 33%.
Reporting
Insert the amount of interest received (and any credit for foreign tax deducted if applicable) on Line 304 of your tax return: