From the Irish International Immigrant Center

Q. I plan to make a couple of short business trips from Ireland to the US in the near future, to meet with contacts, attend an industry convention, and probably do some contract negotiation. Can I do this without applying for a visa beforehand?
A. This should be possible, depending on a few factors. The US government operates what is known as the “Visa Waiver Program” (VWP) for nationals of a number of friendly countries, including Ireland. This program allows travel to the US for up to 90 days for business or pleasure, without applying for a visitor’s visa beforehand. Citizens of Canada and Bermuda are treated essentially the same as those of VWP countries for purposes of short-term visits to the US.
So, first of all, you must be a citizen (not just a resident) of one of the VWP countries. For example, a citizen of Poland temporarily residing in Ireland would not be eligible to travel under the VWP but would need to apply for a visitor’s visa instead, whereas a citizen of Ireland temporarily located in Poland could make use of the VWP.
Second, the business activity involved must fit within the US government’s definition. This does include the activities you mentioned, as well as travel for the purpose of conducting litigation. The permissible activity does not include “employment” (which can be loosely understood as doing work for pay that an American could be doing) while in the US. To work at a job in the US one needs a temporary work visa such as the H1-B or other employment authorization from the US Citizenship and Immigration Services. There are gray areas involved in the definitions of “business” versus “employment,” so if there is any doubt you should consult an immigration lawyer before planning to travel under the VWP.
Third, travelers from VWP countries also need to be personally eligible to take advantage of the VWP. Those ineligible to enter under the VWP because of a visa overstay or other problem, for example, would have to apply for a B-1 (business visitor) visa at the local US Consulate. The permissible business activities are the same for a B-1 visa as with the VWP. The B-1 visa application process takes time and requires a fee, but it has a couple of advantages: it can be granted for up to six months and can be extended, unlike the VWP, which is strictly limited to a maximum of 90 days. Also, a B-1 visa holder can in certain circumstances apply to change status in the US to that of another visa such as a J-1 exchange visa; such status changes are not permitted under the VWP.
US immigration and consular officials can question a traveler both about the business activities planned and the intention to make the stay in the US a temporary one. So, whether traveling under the VWP or applying for a B-1 visa, you should be prepared to document your business trip (your agenda, travel and hotel arrangements, conference programs, contact information, etc.) and your intention to return home within the time allowed (a return air ticket, proof that you are still employed at home, have family and property there, etc.). People used to believe that showing up in a business suit with a briefcase and business cards in one’s pockets virtually guaranteed entry for short business trips. Post 9/11, this is not necessarily the case. So travelers must be prepared for more scrutiny of their intentions.
For a free, confidential consultation about this or any other aspect of immigration law, visit one of our weekly legal clinics as advertised in The Irish Reporter.
Disclaimer: These articles are published to inform generally, not to advise in individual cases. Areas of law are rapidly changing. US Citizenship and Immigration Services and US Department of State regularly amend regulations and alter processing and filing procedures. For legal advice seek the assistance of an IIIC immigration specialist or an immigration lawyer.