Do I need a passport to be valid for a certain period?

What validity do I need on my Irish passport for overseas travel?

This depends on where you're travelling to: 

Ireland

Your Irish Passport must be valid up to your date of entry.  You will, of course, need a valid passport if you are planning to leave Ireland again.

Other countries within the European Union

Your Irish Passport must be valid up to your return date.

Canada

Your Irish Passport must be valid up to your return date. As of March 15, 2016, travellers will need an Electronic Travel Authorization (eTA) before they board a flight to Canada. See Citizenship and Immigration Canada for further details.

United States

Your Irish Passport must be valid up to your return date. You must also get an Electronic System for Travel Authorisation (ESTA) under the Visa Waiver Programme, or a visa, for entry into the United States. You can find more information on the US Embassy in Ireland's website.

All other countries

The passport validity required varies greatly so contact your travel agent or the embassy of the country you are travelling to for the most up-to-date requirements.