The currency of Cambodia is the Riel, although US Dollars is used at most places frequented by tourists and can be used interchangeably for Riel just about everywhere else. While the Riel is theoretically convertible, it isn't commonly traded. Prices at hotels, restaurants and tourist sights are usually in US Dollars. However, businesses in Cambodia don't keep US coins on hand, so small change will usually be given in Riel, at a common exchange rate of 4,000 Riel to one US Dollar.
There are currency exchanges throughout the major tourist destinations, but changing money is more or less unnecessary if you're carrying US notes in small denominations. Automated Teller Machines (ATM) have recently appeared on the scene, although still relatively uncommon. You'll find them in most tourist areas if you look hard enough. Note that ATM's dispense US Dollars, not Riel.
In many cases, this guide can display amounts in the currency of your choice. The current currency selection is shown at the left on every page, and can be changed using the form below. Kindly note that some currencies are not convertible. Conversion rates are updated at least once a week. The conversions shown are approximate values and should be used as a guideline only.