The chapters provide a detailed account of the major issues in the field: foundational questions such as directionality, criteria and parameters of grammaticalization, and phases and cycles; the much-debated issue of the motivations behind grammaticalization, including the role of language contact and typological influences; the advantages and disadvantages of different theoretical approaches; and the relationship between grammaticalization and process such as lexicalization, exaptation, and the development of discourse markers. Each chapter offers guidance on further reading, and concludes with study questions to encourage further discussion; there is also a glossary of key terminology in the field. Thanks to its comprehensive approach, the volume will serve as both a textbook for undergraduate and graduate students and a valuable reference work for researchers in the field.