Notgeld (German for "emergency money" or "necessity money") refers to money issued by an institution in a time of economic or political crisis. The issuing institution is usually one without official sanction from the central government. This occurs usually when sufficient state-produced money is not available from the central bank. Most notably, notgeld generally refers to money produced in Germany and Austria during World War I and the Interbellum. Issuing institutions could be a town's savings banks, municipality and private or state-owned firms.
Notgeld was mainly issued in the form of (paper) banknotes. Sometimes other forms were used, as well: coins, leather, silk, linen, postage stamps, aluminium foil, coal, and porcelain; there are also reports of elemental sulfur being used, as well as all sorts of re-used paper and carton material (e.g. playing cards). These pieces made from playing cards are extremely rare and are known as Spielkarten, the German word for "playing card".
Notgeld was a mutually-accepted means of payment in a particular region or locality, but notes could travel widely. Notgeld is different from occupation money that is issued by an occupying army during a war.
The first large issue of Notgeld started at the outbreak of World War I. Due to inflation—caused by the cost of the war—the value of the material that a coin was minted from was higher than the value of its denomination. Many institutions started to hoard coins. Additionally, the metals used to mint coins were needed for the production of war supplies. This caused a massive shortage of metal for coinage, which was remedied by issuing banknotes in small denominations.