German mediatisation was the major redistribution and reshaping of territorial holdings that took place between 1802 and 1814 in Germany by means of the subsumption and secularisation of a large number of Imperial Estates, prefiguring, precipitating, and continuing after the dissolution of the Holy Roman Empire. Most ecclesiastical principalities, free imperial cities, secular principalities, and other minor self-ruling entities of the Holy Roman Empire lost their independent status and were absorbed by the remaining states. By the end of the mediatisation process, the number of German states had been reduced from almost 300 to just 39.

The Prince-Bishopric of Hildesheim was an ecclesiastical principality of the Holy Roman Empire from the Middle Ages until its dissolution in 1803. The Prince-Bishopric must not be confused with the Diocese of Hildesheim, which was larger and over which the prince-bishop exercised only the spiritual authority of an ordinary bishop.