The Belarusian currency is called "rubel" though Russian variant of the name "ruble" can be (and is) used with relation to Belarusian money.
Currently there are notes ranging from 1 to 50,000 rubles. No coins are used in Belarus for circulation. Only a small amount of commemorative coins is produced.
For the use in metro there are special plastic cards and tokens. Smart cards (plastic cards with microchips) are used for public payphones.
There are not many vending machines in Belarus and if there is one – it would accept paper notes (as do coffee machines at many commercial centers) or tokens will be sold somewhere at a nearby newspaper stand or other small retailer.
There are numerous currency exchange offices in Belarusian cities to change foreign currency to Belarusian rubles and back. Normally there should be no problems with exchanging US dollars, euros and Russian rubles.
Credit and debit cards were not used in Belarus before the last decade of the previous century. And even today the use of plastic cards is rather limited.
Nevertheless, major hotels, restaurants, stores and service outlets accept credit/debit cards issued by Visa and MasterCard. Some other brands can also be accepted but not everywhere
Discovery and American Express cards are not accepted at all
NOTE: Some cases were reported when an issuing bank (US) has frozen a credit card account after some payments were made in Belarus "as a precaution measure". The restrictions were lifted only after a cardholder called back to his bank and confirmed that he actually is making payments in Belarus. Thus, a good idea would be to call your bank in advance and to ask them not to freeze your account when you use your card in Belarus.
There is a growing network of ATMs in Belarus. At present there are almost two hundreds of them in different cities of Belarus. The majority of them are in Minsk (over 50).
Travellers' Cheques of American Express and Thomas Cook are accepted by most exchange bureaus and banks, but not by retailers.
Sending money to Belarus
If you need to send money to Belarus (to friends, relatives, or ask someone to send you some extra money) the fastest and easiest option (though not the cheapest) is Western Union. One can even send money over the Internet using a credit card and a recipient will be able to get the money from one of the numerous bank branches in Belarus.
The other, sometimes less expensive but more lengthy and complex way is to send an international money order or a check. However not all kinds of checks are accepted (e.g. personal checks) and fee for cashing varies from bank to bank (normally 1-5 per cent but not less than US$10).
Please note, that all the money that the residents in Belarus receive from abroad are considered their income and will be reported by the banks to appropriate local tax offices. The recipients of your funds will have to pay taxes on the money they receive.