Notgeld is German for "Emergency Money".
During the early 20th century special money was given out in Germany and Austria to cater for economic crisis situations. This money was not, as normally, issued by the central bank (Reichsbank), but by various other institutions, e.g. banks, municipalities, private and state-owned firms. It was therefore not a legal tender but rather a mutually accepted means of payment.
Notgeld was mainly issued in the form of (paper) banknotes. Sometimes other forms were used, as well: coins, leather, silk, linen, stamps, aluminium foil, coal and all sorts of re-used paper and carton material (e.g. playing cards).
More on [ Notgeld ]

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Bob's Notgeld Page - Images on notgeld categorized by subject.
A Notgeld Collector's Site - Information on collecting German emergency money (Notgeld)
Austrian Notgeld - Collectors of Austrian Notgeld meet here.
Beer related Notgeld - Gallery of German notgeld that has references to beer on it.
Collecting German Notgeld - Personal page of an English collector of German notgeld (1914-1923).
Meta Description: [ A page all about the collecting of German notgeld ]
Karl Falk Collection of German Notgeld - Karl Falk collection of Nazi Der Stürmer newspapers and German notgeld.
Kurioses Notgeld - Unusual Notgeld from Germany Deutschland 1914-24.
Meta Description: [ Kurioses Notgeld Deutschland 1914-24, aus dem Gebiet Papiergeld / papermoney ]
Notgeld During World War I - An exhibition of Notgeld from Germany and Austria-Hungary during World War I, with descriptions. Click on images for enlargements of Notes.
The Notgeld Homepage - Pictures and information on Notgeld from Austria and Germany.