The official currency of Vietnam is Vietnam Dong (VND). In 2010-11, the approximate exchange rate of Vietnamese Dong to US Dollar was around 20,000 VND to 1 US Dollar. Thanks to its low value compared to other major currencies, travel money to Vietnam is kept very affordable. It can take a while to orient yourself towards the zero that you may not have seen before.
Photo: vn.sputiknews.com

Credit and debit cards are not yet common in Vietnam and you should not expect these cards to be accepted at grocery stores and pharmacies. That makes cash the main daily medium of exchange. There are no active coins nor any coin-operated vending machines. The Vietnamese Dong currency has undergone many changes since its first appearance in 1945. The latest version of the Vietnamese Dong is diverse in both colors and denominations. Larger bills are made of polymer and smaller bills are made of cotton.

Related readings:

History of Vietnamese Dong
Banknotes and change
Convert Vietnamese Dong