Although Vietnamese law requires that all prices are quoted in dong, you’ll find many hotels, the more upmarket restaurants, tour agents and so forth still use US dollars and, occasionally, euros. To reflect this and to avoid exchange-rate fluctuations, throughout the Guide we quote prices in the currency used on the spot.
Incidentally, don’t be alarmed if you notice that Vietnamese pay less than you for plane tickets, at some hotels and at certain sights: Vietnam maintains a two-tier pricing system, with foreigners sometimes paying many times more than locals. The good news for tourists is that the system is being phased out, with prices for foreigners being adjusted downwards while those for Vietnamese rise to meet them. A single price system now applies on the trains, for example, while the gap has gradually been narrowing for air travel. It will take several more years before the practice disappears completely, however, and for the moment it remains something of a grey area, particularly as regards hotels and bus tickets, where the amount you pay may well depend on the person you happen to be dealing with.