This might be too much information, but:
We spent 3 weeks in Ireland last summer, and wondered about this too. It was said that you need to have a “pin and chip” credit card to use it in Europe, but that wasn’t the case in Ireland. We used a standard Visa card everywhere with no trouble. Most restaurants used the handheld card reader, so the card never left your sight – they would bring it to the table and complete the bill right there. Visa was easy to use – American Express only worked at 2 hotels.
We also knew that an easy way to get cash is to use an ATM and your debit card, and we had done that before. There was usually no trouble finding a machine – except in the small villages. In one village in Co. Galway, there was only 1 ATM in town, and the day we needed it, it had run out of money! The next morning, as we were leaving, it had not been serviced yet, and we had to drive back to Galway and get our cash and then back to the B&B to pay. We passed several villages that did not have even 1 ATM. In the cities or bigger towns there were usually 1 or 2 on the street front, outside of a bank. The small towns have them inside the gas stations or groceries – they often have a sign outside saying ATM.
One more interesting thing about using the ATM card is that it was the cheapest way to change money. The exchange rate, including the “foreign transaction fee” varied a lot:
BECU debit card -- around 1.33
There was a foreign transaction fee that amounted to just over 1% on each transaction –
taking out 300 Euros had a fee of $2.10, and spending 300 Euros with the Visa card had a fee of $9.51.
VISA card -- this was when paying in Euros -- over 1.36
VISA card -- when paying in US dollars -- around 1.45!
We didn’t know this ahead of time, so when places asked if we wanted to pay in euros or dollars, my husband figured dollars might be best. We didn’t understand the fine print that said they would include a 3.5% exchange rate mark-up. We thought that was the rate we had read that Visa charges anyway, but not so.