Foreign transaction fees are assessed by your credit card bank for each transaction made in currency other than U.S. dollars. This can include internet sites based outside of the U.S.
Not all Chase card products have foreign transaction fees. If you have one, it's outlined in your cardmember agreement.
Tips for using your credit card while traveling abroad
If a merchant operating outside the U.S. offers Dynamic Currency Conversion when you use your credit card at the point of sale, it still may be cheaper to pay with your credit card in local currency and incur the foreign transaction fee, if applicable. For example, let's say you want to purchase a sweater from a British retailer using your credit card; at checkout the retailer gives you the option to process the credit card payment in local currency (£85) or U.S. Dollars ($110). If you choose U.S. Dollars, the merchant has already handled the currency conversion for you. However, if you choose local currency, Visa/Mastercard handle the currency conversion ($105) and your credit card bank assesses a foreign transaction fee (3%, totaling $108.15), if applicable.
Note: all figures and conversions are for illustrative purposes only