Mandan, sole member of one of the four branches of Siouan (within Catawba-Siouan), has under 10 speakers, among some 200 tribal members. Epidemics and inter-tribal warfare reduced these Missouri River village-dwelling horticulturists, from 5000 to under 200 members by 1837. With the Hidatsa (Siouan) and the Arikara (Caddoan), they constitute today's, Three Affiliated Tribes Nation (Ft. Berthold Indian Reservation; North Dakota). Mandan has vocalic epenthesis, is notable for only 10 consonants, 9 vowels (plus length) and no nasal stops, despite nasal spread from 3 nasal vowels. Mandan is a verb-final, head-marking language, with positional auxiliary verbs (sit, stand, lie) marking tense-aspect-modality (these auxiliaries also serve as classificatory NP determiners); other auxiliaries mark diminutives, benefactives and causatives, etc.

Evidentiality, subject-number and other TAM distinctions are mostly suffixal. The verb has active/stative, subject-object split-transitive prefixation and distinguishes addressee gender in its illocutionary suffixation. Coordinate and subordinate clauses suffix a three-way distinction of realis vs. irrealis subject-continuity/switch-reference.