Though Riel (KHr) is the official currency, the US dollar is the common currency in Cambodia. Many businesses, especially hotels, airlines, restaurants, souvenirs shops, set their prices in USD and all expenses can be paid in USD even minor ones. In the West of the country, use of Thai Baht is also commonplace.
At the time of writing exchange rate is US$ 1 = 4040 Riel, and 1 Euro = 4329 Riel (September 2015). You can change Euros into USD, though the exchange rate is not always very competitive. There is no need to change your USD into local currency. Small bank notes of 10 or 20 US dollars are enough. Against payment in USD, the change will be given back to you in local currency as there is no USD cents in Cambodia.
Traveller’s cheques can be cashed only at major banks and usually incur a 2 to 5% transaction fee.
Visa, Master cards, JCB, CCB and American Express are accepted in top-end hotels, restaurants and shops in the main cities of Cambodia, such as Phnom Penh, Siem Reap and Sihanoukville, but can also be subject to 2 to 3% transaction fees.
ATMs (cash dispensers) are now available everywhere in the main towns (Visa, Mastercard). You can withdraw cash in USD only - transaction fees may apply. ATMs from ANZ bank are often available in souvenir shops and in most of the Caltex service stations.
Banks are usually open from 08h00 to 15h30 from Monday to Friday. Only a few banks are open half day on Saturday.
The best advice is to bring US Dollars in cash. Note that exchange rates for small and big notes vary, however we would recommend you to bring some small notes to settle initial expenses and then carry small riel for minor expenses. 500 and 1000 riel are the most useful denominations.
Be careful, banks and foreign exchange offices do not usually take old, scribbled or even stained bank notes.