Credit cards

Your favourite credit card will not be helpful in Cambodia. Credit cards are accepted only at few places like major hotels, restaurants owned by foreigners, souvenirs shops and for a 4 % surcharge.
On the other hand, there is no cash machines in Cambodia.

Traveller cheques

Traveller cheques and currencies other than U.S. Dollars are generally not accepted and if they are only with a high commission.

Dollars

USD is the currency of choice and widely used through the country.

Riel

Riel is the currency of Cambodia The rate of exchange (at time of printing) is 4,000.- Riel to one U.S. Dollar.
Riel does exist in denominations from 100 to 100.000 riel (USD 25) but the most common denomination is the 500 riel bill.