Inflection is the expression of grammatical information through changes in word forms. This confrontation between general principles of syntactic organization and the often idiosyncratic properties of words has brought about systems whose properties—among them an often high degree of complexity—are an important object of investigation in their own right. Because it is something that many languages happily do without, inflection has a curious and often contentious status within linguistics. But even so, there is a fascinating and well-delimited set of facts out there to be explored, for which this handbook will be a guide. The volume is made up of twenty-four chapters, which together take a theoretically ecumenical approach, with particular attention paid to draw the examples from a wide variety of languages. The first section covers the fundamental building blocks of inflectional form and content: morphemes, features, and means of exponence. The second section focuses on what is probably the most characteristic property of inflectional systems, paradigmatic structure, and the non-trivial nature of the mapping between function and form. The third section covers change and variation over time, and the fourth section covers computational issues from a theoretical and practical standpoint. Section five addresses psycholinguistic questions. The final section is devoted to sketches of individual inflectional systems, illustrating a range of typological possibilities across a genetically diverse set of languages from Africa, Asia and the Pacific, Australia, Europe, and South America.