Germanisation (also spelled Germanization) is both the spread of the German language, people and culture either by force or assimilation, and the adaptation of a foreign word to the German language in linguistics. It was a central plank of German liberal thinking in the early nineteenth century, at a period when liberalism and nationalism went hand-in-hand.

Historically, there are very different forms and degrees of expansion of German language and elements of German culture. There are examples of complete assimilation into German culture, as it happened with the pagan Slavs in the diocese of Bamberg in the 11th century.^{[citation needed]} A perfect example of eclectic adoption of German culture is the field of law in Imperial and present-day Japan, which is organised very much to the model of the German Empire.^{[citation needed]} Germanisation took place by cultural contact, by political decision of the adopting party (e.g. in the case of Japan), or (especially in the case of Imperial and Nazi Germany) by force.