The official currency in Cambodia is the Riel. However, United States Dollars (USD) is a widely used currency.
The easiest way to get money is the ATM. Most ATM’s in tourist areas distribute USD, because this is the most common currency. In remote areas, it is difficult find ATM’s. If you take USD from abroad, make sure you have small notes. They usually do not have change from large notes. Sometimes you change partially in USD, partially in Riel.
VISA and MASTERCARD are widely accepted in tourist areas, especially in hotels, better restaurants and shops. You need a pin code and sometimes there is a surcharge of 3%.