Numismatics
Numismatics is the study and collecting of money. Although I have collected some coins, my main interest is paper money. Because I collected militaria before money, I am especially interested in items that have some military relationship, such as occupation money, military payment certificates, and POW and concentration camp scrip.
A great reference for this field, whose title captures the essence of why many of us collect, is World War Two Remembered: History in Your Hands – A Numismatic Study, by C. Frederick Schwan and Joseph E. Boling, published in 1995.
Early Notes
Among the earliest examples of paper money were notes issued during the French Revolutionary period. Because these were quickly devalued, many were never issued and high quality examples survive to this day.
French Revolutionary Note - 25 Livres (1793)

10 Paoli note from the Roman Republic, a state established by Napoleon

Polish 50 Zloty note (1794)

World War One Examples of POW camp notes from Austria-Hungary and Germany.
Among the Austrian notes is one from the POW camp at Theresienstadt, whose most famous prisoner was Gavrilo Princip, the assassin who shot Archduke Ferdinand in Sarajevo in July 1914, precipitating the First World War. Theresienstadt would gain infamy in the Second World War as the site of the Nazi model ghetto for Jews.
World War Two U.S. Guerrilla Money from the Philippines - 2 Pesos, Negros Island

Examples of German Armed Forces military payment certificates:

German occupation note from the Reich Protectorate of Bohemia-Moravia, now the Czech Republic

German occupation note from Poland, with stamp from the Polish Home Army

German occupation note from Ukraine

Reverse of the same note
