Vietnam Dong
The official currency in Vietnam is the Vietnamese Dong (VND). However, most hotels and bigger shops also accept US dollars, for taxis and more local places most people would much prefer to be paid in Dong, so it is important to keep a good supply of local currency while travelling in Vietnam.
Continuing inflation and a series of devaluations continues to steadily push down the value of the dong, with USD1 worth over 22,000 dong in May 2016. Banknotes are available in denominations of 500, 1000, 2000, 5000, 10,000, 20,000, 50,000, 100,000, 200,000 and 500,000 dong. In 2003, coins were also introduced in denominations of 200, 500, 1000, 2000 and 5000 dong, although these are rarely seen
Money
You cannot purchase Dong outsite of Vietnam, so you should change money on arrival and get rid of any leftovers before leaving the country. The advise is to change money at official money exchange counters to get the fair rate, there is an official money changer at Da Nang airport.
Some high-end hotels also offer money exchange services with a lower rate. You should avoid the illegal exchange places such as gold shops.
For credit card payments there is usually a 3% surcharge, so cash may be better for larger transactions
Travellers cheques of well known companies are widely accepted, but usually a small fee is charged
ATMS are becoming more and more common and can be found in most bigger cities and every tourist destination. There is definitely at least one on Le Loi, which is the main street in the old town. Typically withdrawls are limited to 2,000, 000 dong per transaction, which will incur a 20, 000 dong service fee
When we went in March 2016 we used a combination of US dollars to change and also a preloaded currency card. We used the US dollars to pay for tailoring and Vespa Tours.
There are different types of currency cards, ones that you preload in a particular currency, ie US Dollars, or ones that you load in your own currency and can use anywhere in the world. Personally, I would recommend the later, but check the rates, and to have the ability to be able to load via the internet is a requirement.