If you have a parent or grandparent who was born on Irish soil, it is definitely worth it to consider dual citizenship. If it is your parent who was born in Ireland, but you were born elsewhere, you already are an Irish citizen and only need to fill out the paperwork.
However, if you are like me, my parents were both born outside of Ireland--but I still had that Irish grandmother. This is where you can receive citizenship through decent. You do this by adding your birth to the Foreign Births Register in Ireland.
Once you are an Irish citizen, your children will be entitled to Irish citizenship (but only if they weren't born when you registered). Then they, too, can register into the Foreign Births Register before having children and succeed in maintaining citizenship through the generations.
The effort can take awhile--you have to dig up birth certificates and wedding certificates for each generation. For your Irish grandparent, this can mean that you have to purchase documents from Ireland and have them mailed to you. Once you submit your application, it can take 4-12 months before you receive your citizenship in the mail. It is worth the effort, because if you allow a generation to pass without getting citizenship, your family loses the right to claim citizenship.
The website http://www.inis.gov.ie guides you on how to fill out your paperwork and begin the process of becoming a citizen.
