Personal pronouns in Japanese form a heterogeneous category. This book investigates their historical development from a functional perspective. It shows that while nouns give rise to personal pronouns through semanticization of pragmatic inferences, the use of non-nominal forms such as demonstratives and reflexives for person referents can be resolved within their original functions, offering little reason to treat them as personal pronouns. The cross-linguistic investigation into the common sources of personal pronouns reveals that the development of personal pronouns from nouns is largely consistent with grammaticalization, but that of forms of non-nominal origins requires separate mechanisms such as spatial/empathetic perspectives and displacement of semantic features for politeness, showing that a one-size-fits-all approach to diachrony of personal pronouns is not sufficient. This book will be of special interest to researchers and students in historical linguistics, pragmatics, and Japanese linguistics, who take a functional view of language.