Travelling to the USA - Do you need a Visa?

Generally speaking you won't need a Visa if you hold a full UK or Irish passport.

However, if you are Irish with a UK passport make sure that on the page with your photo it says British Citizen and NOT British Subject. Subjects DO need a Visa.
(note this differentiation doesn't occur on an Irish passport as everyone is classified as a Citizen)

Note that after October 2004 you must also possess a machine readable passport. This is easily identified by looking at the the page with the photo. At the bottom of the page are two rows of black print that includes your name and lots of numbers