The currency in Maldives is the Maldivian Rufiyaa and is non-convertible, so it cannot be purchased in advance. The currency is available in denominations of 500, 100, 50, 20, 10 and 5 Rufiyaa notes. You can carry the US Dollar and can be used within Maldives. You can also exchange currency at the airport at the Bank of Maldives Foreign Exchange counter, which is the only dedicated foreign exchange counter.
If you do use USD for transactions, keep in mind that some businesses do not accept old or defaced notes. Also, the change will be given back will be in Rufiyaa and not the dollar. You can also use your credit or debit cards for transactions but will be charged additional taxes on the same.
Before you head out for your Maldives tour, check with the foreign exchange at SOTC for the best advice.