I spent the past few weeks in Italy and the U.K., and didn't have any luck using Apple Pay. I tried using both a Visa and Discover card on the London Underground and the transactions didn't go through. This happened in other places around London as well. I asked customer service at the London Underground if I could use my U.S. card through contact-less payments and they advised me to not use it for some reason. My guess is that if you have a credit card with Apply Pay that is supported in both the U.S. and the country you are in, it would work. The Visa from my bank and Discover aren't on the official U.K. list on the Apple Pay support page, so I could be totally wrong with that guess, but it was the only thing that made sense to me with the transactions not working at all. From my experience, Italy had very few NFC terminals, at least where I was. So do feel free to see if you have any better luck, but that was at least what I saw happen very recently.