Being an island of dual identity, there is also a choice of currencies. The official currency of Sint Maarten is the Antillean Guilder or Florin (fls). The Guilder is pegged to the US-Dollar and not free floating. The exchange rate is approximately 1.80 fls. for 1.00 $-US. IMPORTANT: Prices in the supermarkets and gas stations on the Dutch side are given in Guilders, but most other prices are quoted in US-Dollar.
The French side of the island is part of the European Union and uses the Euro, the currency of the EU. At the time of this writing 1 US-Dollar buys 0.95 Euro. And for 1 euro, you'll get 1.05 US-Dollar. Many vendors on the French side offer a 1 to 1 exchange rate. It might be wise to always carry a few Euros once the Europpean currency gains in value again. It has been up as high as $1.45.
The US Dollar is accepted on both sides of the island and is in fact the most common currency on St. Martin/St. Maarten. ATM machines can be found everywhere, both on the Dutch and French side. They are located at banks, supermarkets and even inside gas stations. Most ATM card systems common in the US and Europe are accepted and it is not necessary to bring large amounts of cash to your vacation. All major credit cards are widely accepted.
IMPORTANT! Most ATM are able to disberse several different currencies! You might be asked on the screen in what currency you wish to complete the transaction.