International credit and debit cards cannot be used in Iran since the system is not connected to international banks. Visitors cannot draw cash on credit or bank cards (such as Cirrus or Maestro). Iran does have an international network of ATMs but used within locally-issued bank cards issued by local Banks.
The Iranian Rial (code IRR) is the currency of Iran. Although the “Toman” (tumân) is not an official unit of Iranian currency, Iranians commonly express amounts of money and prices of goods in “Tomāns”. Accordingly, one “Toman” equals 10 Rials. Despite this usage, amounts of money and prices of goods are virtually always written in Rials. For example, the sign next to a loaf of bread in a store would state the price in Rials, e.g., “10,000 Rials,” even though the clerk, if asked, would say that the bread costs “1000 Tomāns”. There is no official symbol for the currency but the Iranian standard ISIRI 820 defined a symbol for use on typewriters (mentioning that it is an invention of the standards committee itself) and the two Iranian standards ISIRI 2900 and ISIRI 3342 define a character code to be used for it. The Unicode Standard has a compatibility character defined U+FDFC ریال Rial sign (HTML ﷼). In December 2016, the Iranian government announced the country’s currency will be changed from the Rial to the commonly used Toman. It needs the Iranian Parliament’s approval. Coins are issued in values of 50, 100, 250, 500, 1,000, 2,000 and 5,000 Rials with banknotes produced in 500, 1,000, 2,000, 5,000, 10,000, 20,000, 50,000 and 100,000. If you remember that a yellow IRR50,000 note was approximately equal to a euro you wouldn’t use to get confused. For large amounts you will see Iran Cheques being used, in IRR500,000 (c. USD15) denominations. They’re now used in the same way as cash.
There is a currency exchange office at the new Imam Khomeini International Airport in Tehran as well as several more in the center of Tehran and other big cities. A network of currency exchange offices operates in Tehran and in major cities under the license of Iranian Melli Bank (Bank-e Melli). Many banks also offer foreign exchange facilities, but not in all branches. Your host and hotel staff should be able to advise you further.