The monetary unit of the Dominican Republic is the Dominican Peso (RD$ / DOP). The exchange rate fluctuates but right now it is: one US dollar is approximately RD$ 42.00 as of September 2013.
The best exchange rate is obtained when changing CASH US Dollars to Dominican Pesos. Euros, Pounds, Canadian Dollars and other currencies do not get the best rate.
Most hotels, restaurants and businesses accept major credit cards and are charged the official rate at the time of the transaction.
In the banks, you are also able to obtain cash from credit cards but make sure you have some form of identification with you.
Please avoid the black marketers, who will offer you a tempting rate of exchange for your US dollars. This is illegal and it is easy to get ripped off.