One of the interesting aspects of visiting both Vietnam, a developing socialist country, and Japan, a modern industrial power, in the same trip is the ability to contrast the two cultures and economies.
Well, the currency is a great place to start. Vietnam has obviously had at least one round of hyperinflation in the past since the conversion rate between the dong (VND) and the dollar (US$) is 15,000 to one. The actual government set rate is around 15,800 to 1, but most merchants and stores round down to 15,000 in their benefit any chance they get.
The smallest denomination of currency is the 1,000 VND note (~US$0.07), although coins are more common in this range. The largest note is for 100,000 VND (~US$6.50) and bills for 5,000, 10,000, 20,000 and 50,000 VND are also very common. The problem is that with all the zeroes on the currency, telling them apart requires more concentration than it should. Pulling out a 50,000 VND bill when you want a 5,000 and vice versa happened way too often.
The relatively small value of the biggest bill was not that big of a problem since relatively few things cost more than 100,000 VND. A bowl of pho (a popular meal-sized soup) cost around 20,0000 VND (~US$1.50). At most small cafes, a meal for three got change from a single 100,000 bill.
For bigger purchases, and many smaller ones, US currency was accepted and even preferred. Some merchants would only quote dollars to obvious foreigners like myself. This policy is officially frowned upon, but nearly ubiquitous. I was able to buy 7 arcade game tokens with a single one dollar bill. The price of a high quality silk tie was US$5 nearly everywhere. A little money went a long way in most circumstances.
Japan, on the other hand, was a completely different story. Japan deservedly has a reputation as a very expensive country and the currency reflects it. The yen has been pretty steady for many years at about 110 yen to the dollar. Once you embrace the concept of a yen being about a penny, everything makes sense (no pun intended).
The smallest available bill is the 1,000 yen note (~US$10). It's a little unnerving to buy a soft drink from a fast food place with the equivalent of a ten dollar bill and only get change back. The 500 yen coin seems to be a relatively new item since many vending machines couldn't or wouldn't accept it.
As I left the country, my goal was to spend all the 100 yen coins I had accummulated over the few days I was there. With soft drinks and candy snacks at about 150 yen each, or about as much as a whole meal did in Vietnam, that didn't take long.
So in summary, the smallest bill in Japan is worth more than the largest bill in Vietnam. And the dong goes a lot further than the yen.