It depends. If you were born outside the island of Ireland and if either of your parents was an Irish citizen who was born in the island of Ireland, then you are entitled to Irish citizenship, and entitled to apply for an Irish passport under Irish law, irrespective of where you reside.
You can also apply for Irish citizenship if one of your parents, while not born in the island of Ireland, was an Irish citizen at the time of your birth. In most cases applications of this type are made through a grandparent who was born in Ireland. In this case, you will need to register your birth on the Foreign Births Register. This is a separate application and must be completed before you can apply for your passport.
You may also qualify if one of your parents obtained Irish citizenship through Naturalisation or Foreign Birth Registration before you were born. In these cases, Irish citizenship can be passed on to the next generation as the parent was an Irish citizen at the time of the applicant’s birth. Citizenship by Foreign Births Registration applies only from the date of registration. Only Irish citizens may hold an Irish passport, but it is not necessary to have an Irish passport to be an Irish citizen. Click here for more information on the Foreign Births Register.