The Cambodian currency is the riel, but the U.S. dollar is nearly as widely accepted, and many high-end businesses actually require payment in dollars. All prices are given in dollars. Thai baht are usually accepted in bordering provinces.
The official exchange rate is approximately 4,000 riel to one U.S. dollar and 100 riel to the Thai baht. It's possible to change dollars to riel just about anywhere. Banks and businesses usually charge 2% to cash traveler's checks.
ATMs are available in Phnom Penh, Siem Reap, and Sihanoukville, mostly at ANZ and Canadia banks, although there are a few other banks starting to install them. Credit cards are accepted at major hotels, restaurants, and at some boutiques. Cambodian banking hours are shorter than in many Western countries, generally from 8 am until 3 or 4 pm. ATMs are available 24 hours.