Romania's currency is the leu (usually appears in the plural form lei). It comes in Polymer notes.

The currency has changed to RON (Romanian new lei). 

1 (green) 5 (purple) 10 (Reddish Brown) 50 (Yellow) 100 )Blue) (200 and 500 lei notes are rarely used).

The leu's subdivison is the ban (plural form bani), 1 leu = 100 bani), which comes in 1 (brass), 5 (cooper) 10 (steel) and 50 (brass) bani coins.

Euros are often accepted (especially for larger and legal transactions and you may frequently see prices quoted in euros e.g. for Houses and Land)) other Foreign currencies are usually not accepted; some hotels and tourist shops do take major international currencies (Euros, GBP CHF DKK SEK NOK USD etc.), but the exchange rates they offer are frequently lower than the normal rates.

Exchanging money

If you want to change some money, the primary option is to use ATMs. Using ATM cards is very convenient and safe. You get a better exchange rate at exchange offices but take care as some (very rare) charge a % which subtract from value received (just look for word COMISION which have to be 0%). Prior to make the exchange they have to give you a receipt which you have to sign so if anything is fishy you may say you don't want to exchange anymore, just ask for you money and leave. The big advantage of using ATM machines is that they eliminate the need to carry large amounts of cash as traveller's checks are virtually useless in shops.

Some Debit cards give a poor rate of exchange and some charge a fee for each transaction so taking out larger amounts is sometimes a better option. 

Surprisingly, currencies from bordering countries are hard to exchange and not used - even from romanian speaking Moldova! (you'll be lucky to get 50%) - Ukrainian Grivna and Serbian Dinar are difficult, even Bulgarian Leva and Hungarian Forints will "lose" you 30% unless you change at the border.

If you use exchange offices always check the commision percentage, usually it is zero except in the airport.

The ATM works fine and you can find them almost in all big shops locations, sometimes near public institutions and ofcourse at banks external wall. Also the big shops accept Visa and Mastercard.

If you're in Bucharest your best place to shop for exchange rates is Calea Mosilor (pron. Moshilor) near Bucur Obor. Many good exchange bureaus there. Just check there is 0% commission, and read carefully the exchange rate for your specific amount of money and don't mismatch with traveler checks rates. If you feel unsure, write down on a piece of paper both the amount of money you have and the exchange rate, and show it to the clerk. The nastiest trick (perfectly legal) is to offer a very good rate for big amounts of money and a much lower one for small sums, written in tiny fonts. Careless customers pay dearly for their mistake. Never accept unregistered transactions, always ask for your receipt. You have to hand the clerk your passport or another ID with photograph. Check exchanged money inside the premises, in front of the clerk.

If you do plan on exchanging cash be sure you have brand new bills with no cuts or marks of any kind on them. Usually exchange houses will not take bills with bank marks or other markings on them. Even a small tear in a bill and it will be rejected. If you are using Euros or Pounds be sure you have only the most recent design and coloration on the note.