The standard voltage is the Republic of Ireland is 220 VAC at 50Hz.
Plugs are 3 pin 1363 type.
Most shaving sockets also support 110 VAC with the 2 pin international shaving plug and are to be only used for shavers.

The voltage in Northern Ireland is 230/240 VAC 50Hz.

If you're coming from America ( 110V ) you'll need step down transformers and adaptor plugs.
If you're moving from continental Europe, you're likely only to need adaptor plugs.