The Army of the Holy Roman Empire (German Reichsarmee, Reichsheer or Reichsarmatur; Latin exercitus imperii) was created in 1422 and came to an end when the Holy Roman Empire was wound up in 1806, as the result of the Napoleonic Wars. It must not be confused with the Imperial Army (Kaiserliche Armee) of the Emperor.
The Army of the Empire did not constitute a permanent standing army which was always at the ready to fight for the Empire. When there was danger, an Army of the Empire was mustered from among the elements constituting it, in order to conduct an imperial military campaign or Reichsheerfahrt during an Imperial War (Reichskrieg) or an Imperial Execution (Reichsexekution). In practice, the imperial troops often had stronger local allegiances than their loyalty to the Emperor.
Prompted by the threat posed by the Hussites, the Imperial Diet of 1422 held in Nuremberg created the Army of the Empire by demanding specific contingents of troops from the various parts of the Empire. The Hussite Wars continued from 1420 to 1434, by which point the army had proved its worth. Over the next hundred years, the size of the Army was controlled either by the number of serving men being strictly regulated or by limits on the money that paid for it. At the Diet of Worms in 1521 a commitment was made to keep the strength at 20,063 infantry and 4,202 cavalry. This was later simplified to 20,000 and 4,000. The monthly cost of paying for an army of this size was known as the Römermonat. The Imperial Register (Reichsmatrikel or Heeresmatrikel) determined the contributions of the individual states making up the Empire, the first being the Register of 1422.