Yes you will definitely need a passport to travel from US to Ireland or vice versa. Also a visa probably, especially if you intend working. Contact the Irish embassy re visa requirements.
Ahhhhh brilliant! I love it! nickjahn has a pop at jenstar for cracking a joke.....word of advice, nickjahn, if you don't want people to make jokes at your expense, then don't ask such idiotic questions. Of course you need a passport.
The idiot is back one more time. Where are you people from anyway? Part of the world that hates Americans(there are valid reasons for that, I know)? I hardly ever travel, so I really didn't know the answer to my question. Also, when travelling to Canada or Mexico from the US, you do not need a passport.