Travel Question.

An American relative of mine is off to Germany to see a few other relatives over the New Year. To cut a long story short, he's always been talking about wanting to visit Ireland. Since we come from such a swell and generous family, we were thinking of surprise-flying him over to Ireland after spotting a good deal on Aer Lingus. Just wanted to ask, would there be a problem with him coming over here visa-wise or would he be good to go with just his passport? Oh, if you book online with Aer Lingus to they send you out real tickets or issue you with those e-jobbies?

I know there's a travel forum, just thought it would get more replies here, feel free to shift though.