German mediatisation (English: ; German: deutsche Mediatisierung) was the major territorial restructuring that took place between 1802 and 1814 in Germany and the surrounding region by means of the mass mediatisation and secularisation of a large number of Imperial Estates. 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 into the remaining states. By the end of the mediatisation process, the number of German states had been reduced from almost 300 to just 39.

In the strict sense of the word, mediatisation consists in the subsumption of an immediate (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 mediatisation for the entire restructuring process that took place at the time, whether the mediatised states survived in some form or lost all individuality. The secularisation of ecclesiastical states took place concurrently with the mediatisation of free imperial cities and other secular states.

The mass mediatisation and secularisation 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.