German mediatization (English /miːdiətaɪˈzeɪʃən/; German: deutsche Mediatisierung) was the major territorial restructuring that took place between 1802 and 1814 in Germany and the surrounding region (until 1806 the Holy Roman Empire) by means of the mass mediatization and secularization of a large number of Imperial Estates: ecclesiastical principalities, free imperial cities, secular principalities and other minor self-ruling entities that lost their independent status and were absorbed into the remaining states.
In the strict sense of the word, mediatization consists in the subsumption of an immediate (German: unmittelbar) state into another state, thus becoming mediate (mittelbar), while generally leaving the dispossessed ruler with his private estates and a number of privileges and feudal rights, such as low justice. For convenience, historians use the term mediatization for the entire restructuring process that took place at the time, whether the mediatized states survived in some form or lost all individuality. The secularization of ecclesiastical states took place concurrently with the mediatization of free imperial cities and other secular states.
The mass mediatization and secularization of German states that took place at the time was not initiated by Germans. It came under relentless military and diplomatic pressure from revolutionary France and Napoleon. It constituted the most extensive redistribution of property and territories in German history prior to 1945.
The two highpoints of the process were the secularization/annexation of ecclesiastical territories and free imperial cities in 1802–03, and the mediatization of secular principalities and counties in 1806.