Currency

When bartering for goods and services no longer meets the needs of commerce, the sentient beings of the Realms turn to using items with a more universal value, namely precious metals, gems, and some minerals. Metals are rarely found in their pure form in nature and require significant energy and effort to refine and purify them. In general, the rarity and the amount of effort it takes to produce a given metal determines its worth. Sometimes this formula is modified by a particular property of the metal, or by a widespread use (and therefore greater demand). The penalty for counterfeiting is death in most places because cities, kingdoms, and nations rely on the acceptance and trust of their currency.

Gems are even rarer than metals and require great skill in mining, cutting, and polishing. Gems have great value because people desire them for their beauty and often wear them in jewelry. The arcane Arts also require certain gems as spell components which increases their rarity even more as they are consumed in the casting of powerful spells.

1st Edition Currency
In the 1st Edition Forgotten Realms Campaign Set the kingdom of Cormyr is used as a representative example of a location with a standard system of currency. The names and values of the various coins are:

This valuation system is prevalent but not ubiquitous throughout the Realms.

Cormyr
The royal coinage of Cormyr is stamped with a dragon on the obverse and a treasury date mark on the reverse. There is no paper currency other than I.O.U.s which are known as "blood-notes" because they must be signed in blood by all parties involved and taken to the local Lord for the affixing of the royal seal.

Silver Marches (Luruar)
Silverymoon mints its own coin, the moon. It is valued at 2gp and is accepted throughout the Silver Marches.

Waterdeep
In Waterdeep a toal is a coin that is worth 2gp in the city but practically worthless outside the city. The toal is a square brass coin with a hole in the center to allow it to be strung on a string.