Quechuan is a family of closely related indigenous languages spoken in Argentina, Bolivia, Colombia, Ecuador, and Peru, in the central part of the Andean cordilleras, in what used to be the Empire of the Incas and adjacent areas. It is divided into two main branches, commonly denominated Quechua I and II, and comprises 15 or more spoken varieties and several extinct ones that can be considered separate languages, although an exact number cannot easily be established. Quechuan shares a long and intense contact history with the neighboring Aymaran languages, but a genealogical relationship between the two families has never been demonstrated, nor a relationship with any other language family in the area. Quechuan languages are mainly agglutinative. All grammatical categories are indicated by suffixes with very few exceptions. The order in which these suffixes occur within a word form is governed by rules and combinatory restrictions that can be rigid but not always explicable on a basis of scope and function. Portmanteau suffixes play a role in verbal inflection and in mutually interrelated domains of aspect and number in the Quechua I branch. In Quechuan verbal derivation affixes may be semantically polyvalent, depending on the combinations in which they occur, pragmatic considerations, the nature of the root to which they are attached, their position in the affix order, and so on. Verbal derivational affixes often combine with specific verbal roots to denote meanings that are not fully predictable on the basis of the meaning of the components. Other verbal affixes never occur in such combinations. Verbal morphology and nominal morphology tend to overlap in the domain of personal reference, where subject and possessor markers are largely similar. Otherwise, the two morphological domains are almost completely separate. Not only the morphological inventories but also the formal constraints underlying the structure of verbs and nouns differ. Nominal expressions feature an elaborate but relatively instable system of case markers, some of which appear to be of recent formation. Transposition from one class to another, nominalization in particular, is indicated morphologically and occupies a central place in Quechuan grammar, particularly in interaction with case. Finally, there is a class of Independent suffixes that can be attached to members of all word classes, including adverbial elements that cannot be classified as verbs or nominals. These suffixes play a role at the organizational level of larger syntactic units, such as clauses, nominal phrases, and sentences.