Cambodia's currency is the riel.

Bills are available in the following denominations:

100 200 500 1000 2000

There's little point in carrying around much riel as US dollars are as readily accepted as the Cambodian riel; in fact, dollars are usually preferred. The riel is most often used in lieu of coins since 1000 riel is roughly equal to a quarter. The Thai baht is almost as widely accepted as the dollar. Vendors are accustomed to accepting both foreign currencies and are always aware of the current exchange rate. In many establishments, particularly restaurants, it's not uncommon to make a purchase using all three currencies!

When accepting US currency in Cambodia make sure the notes are not torn or faded. Even the slightest tear in a US note renders it worthless. (This isn't the case for the Cambodian riel as most of the notes seem to have been in circulation since before Angkor Wat was built!)

Banks will gladly change US dollars into riel. Moneychangers also hang around the markets in Phnom Penh, Siem Reap and Sihanoukville. Toward the end of your stay in Cambodia spend whatever you've got left in riel, because the currency is worthless outside the country. It cannot be exchanged into another currency and isn't traded internationally. So anything you leave with is nothing more than a souvenir.

Travelers checks and plastic are not widely accepted. Travelers checks denominated in US dollars are preferred - and even then are difficult to cash outside Phnom Penh or Siem Riep. If traveling in the provinces forget the checks and carry cash. Credit cards are accepted at only the best hotels in Phnom Penh and Siem Reap. There are no ATM machines to be found anywhere in Cambodia. Credit card cash advances (even on check/debit VISA ATM cards) can be done at Cambodian Commercial Bank branches in Phnom Penh, Siem Reap, Sihanoukville and Battambang. All currency is issued in US dollars only. Expect to pay a minimum of 2% commission to cash a travelers check or take a cash advance.