Yes, you can use US Dollars (USD) in St. Lucia, and they are widely accepted across the island, especially at resorts, restaurants, and tourist-heavy areas like Soufrière and Rodney Bay. However, the official currency is the Eastern Caribbean Dollar (XCD), which is fixed to the US Dollar at a rate of $1 USD = $2.70 XCD. While you can pay in USD, be aware that you will almost always receive your change in EC Dollars. Furthermore, local shops and "mom-and-pop" vendors may give you a less favorable exchange rate (often $2.50 or $2.60) to account for the bank fees they pay to convert it. For the best value, it is recommended to use the local currency or a credit card for larger purchases. Taxis and street vendors often quote prices in USD, so always clarify which currency is being discussed before agreeing on a price to avoid paying nearly triple the expected amount!