Pay for an item using a debit card. The cost will be converted into euros and your bank statement will reflect this. You may also use your debit card to withdraw euros at an ATM, but be aware that you will charged international ATM fees.
Use a credit card if the vendor accepts your credit card provider. There may be international usage fees.
Apply for a PayPal debit card (see Resources). The card can be used anywhere that accepts MasterCard. It's good worldwide, and you can earn up to 1% cash back on qualified purchases.
Convert your dollars to euros at a currency exchange. Because Italy is part of the European Union, the euro is the accepted form of currency. Avoid exchanging at airports where the exchange rate is not in your favor.
Use American dollars at street markets. Even though the euro is used almost anywhere, street vendors may be more forgiving if you only have dollars. Know that you may not get a good deal because you do not have their preferred currency.
