The Vietnamese dong (VND), Vietnam’s official currency, come in polymerized and cotton notes with multiple zeroes: VND 10,000 is the smallest polymer bill you'll find on the street these days, however, there are still cotton 1000, 2000, and 5,000 bills in circulation. The highest banknote that you'll find is the VND 500,000 bill. 

At the present exchange rate (between 20,000-21,000 VND per US dollar), changing a fifty-buck note gets you 1.172 million dong. 

Where to Change Your Money

Major currencies can be exchanged practically anywhere in Vietnam, but not all exchange facilities are created equal. Banks and airport moneychangers can change your money at a high cost relative to a jewelry shop in Hanoi's Old Quarter, so it pays to ask around before trading dollars for dong.

• Banks. The government-run Vietcombank can exchange dong for US dollars, Euros, British Pounds, Japanese Yen, Thai Baht, and Singapore dollars. Banks in major cities like Hanoi and Ho Chi Minh City will let you change foreign currencies and most travelers' checks. You'll be charged a commission rate of between 0.5 to 2 percent for the latter.

• Hotels. Your mileage may vary with hotels: larger hotels can offer rates competitive with banks', but smaller hotels (like those in the Old Quarter of Hanoi, or those near some of Vietnam's top beaches) may tack on an additional fee for the service.

• Gold and jewelry shops. The rates in these mom and pop establishments can be surprisingly fair, with no fees (unlike those in hotels and airport bureaux de change). Shops in Hanoi's Old Quarter—particularly Hang Bo and Ha Trung streets—offer better deals, as do gold and jewelry shops in Ho Chi Minh City's Nguyen An Ninh Street (near Ben Thanh Market).
• Finding and Using ATMs: You're certain to find an ATM to withdraw from in any of Vietnam's major cities, but smaller towns have also begun to support.
• Using Credit Cards: Cash rules in Vietnam, though credit cards are accepted in many restaurants, hotels, and shops in Vietnam's big cities. Visa, Master Card, JBC and American Express are the most common credit cards honored in Vietnam.

Can US Dollars Be Used?

Not very often. Shops that used to accept payment in dollars are now obliged to ask for payment in the local currency only. You're better off exchanging your money at banks or other authorized currency exchange centers. Besides, paying in Vietnamese dong gets you better value than paying in dollars. Better to spend day-to-day using VND, while keeping a stash of dollars around for emergency purposes only.