This introduction centres mainly around a discussion of the theory, methods and work-fields of research into grammaticalization and its application to selected problems of German. The following theoretical aspects are dealt with: distinctive features of grammatical signs, the structure of grammatical categories, degrees of grammaticalization, grammaticalization scales, cognitive and communicative strategies, grammaticalization cycles, and the links between grammaticalization theory and research into language change. Four extensive case studies on the German language revolve around grammaticalization phenomena in connection with modal verbs, the passive with bekommen, prepositions, and modal particles.