Do I need to show a round trip ticket when traveling to Ireland/Northern Ireland?

I don't think it would be an issue. I never heard that, what Aine said about people from Northern Ireland not liking it referred to as Northern Ireland. Any Northerners I ever met were quite upfront about saying they were from Northern Ireland, so what Aine says is news to me.

As far as I am aware, you can stay up to three months without a visa, so be sure you don't exceed that, and of course as advised keep a hold of all your documentation just to be on the safe side. In terms of the other issue raised, not sure where Aine is getting her info from but as Orla C says, Northern Ireland is, as it stands, the name of the country.I've never heard anyone take exception to it. I live here and personally couldnt care less if you call it Ireland, Northern Ireland, the north of Ireland etc because I use all myself. Generally I just say I am from Ireland unless someone asks me to specify (usually because they realise my dulcet tones are not quite what they were expecting of an Irish accent :) )

I would imagine as American you would have little issue with immigration etc. If you were Brazilian etc then I would imagine there would be some questions to answer on arrival. Usual questions that immigration ask are, proof of where yo will be staying, evidence that you have sufficent money in cash or in bank to sustain your stay. To be honest though, when immigration from Republic see that you intend to travel North they will not be so strict as they view any potential problems as a British Issue and ot an Irish one. Also should be no problems referring to Northern Ireland!

Consider buying an open ticket, will allow to go back anytime within 90 days. I think you might need a visa if you're going to stay for more than 3 months in Republic of Ireland...

I really doubt it, but I would bring some sort of travel receipt just in case. Just print your tickets and have them handy. Just a little tip. Don't refer to the north of Ireland as 'northern Ireland' when you visit. Not a good idea lol. There are very few Irish people who would say they are from 'northern Ireland', you'd be safer to just refer to Ireland as Ireland. ;-) Good Luck & enjoy! Aine

You shouldn't have any problem, I have done the same myself and am American as well. It's an open border, and if you get an open return ticket, your bases are covered. The airport in Belfast is small but nice, you can get a connecting shuttle flight from there cheaply to a few places if you are traveling around the UK. Call your airline to be sure and make the arrangements as needed, but otherwise it won't be an issue. As previously said above, Irish immigration has no issues with Americans in general. You'll just get the basic questions, if that. Safe trip.