AD>Grammaticalization theory has played a major role in the developments in language typology and functional linguistics during the last three decades. Grammaticalization phenomena show that grammars evolve in a continuous way following cross-linguistically established diachronic paths. The contributions in this book shed new light on some central issues in grammaticalization theory such as the (uni-)directionality debate, the relation between grammaticalization and constructions, and the concept of multiple grammaticalization. Evidence for grammaticalization in several domains of grammar is presented: adpositions, numeral classifiers, honorifics, agreement markers, applicatives, reciprocals, delexical verbs, auxiliaries, relative clauses, and discourse particles. The empirical investigations come from several languages, among them many understudied languages such as Nanafwe, Maltese, Manambu, Chibchan and Siouan languages.