The Pirahã language is spoken by the people of the same name. They live in Brazil, along the Maici river, a tributary of the Amazon.

The Pirahã language is phonologically the simplest language known, having just ten phonemes, one less than in Rotokas. Its phonemes are:

                 Bilabial  Alveolar  Velar   Glottal
Voiceless stop   p         t         (k)+    x
Voiced stop      b                   g
Fricative                  s*                h

Vowels a o i

+ high tone

+ /k/ is believed to be an optional portmanteau of /h/ and /i/. * /s/ is used only by men; /h/ is substituted by women.

The total number of phonemes is just 11 if /k/ is counted as a phoneme; if not, then men use 10 phonemes, and women just 9 (English, by comparison, has 40). However, many allophones of these phonemes exist; /b/, for instance, has as allophones a bilabial nasal (equivalent to English /m/) and bilabial voiced trill, and /g/ has a highly unusual double flap that is so far unique to this language.

The SAMPA equivalents of the phonemes are:

/p t k ? b g s h a i o/

Pirahã is agglutinative, using many affixes to communicate meaning. A lot of verbs in Pirahã are affixes, particularly verbs of existence or equivalence. For instance, the Pirahã sentence "there is a paca (a type of mammal) there" uses just two words:

káixihíxao.xaagá         gáihí
paca      .poss-exist/be there

Pirahã also uses suffixes which communicate evidentiality, a category of grammar which English totally lacks. One such suffix, /-xáagahá/, means that the speaker is completely certain of his or her information:

 hoagaxóai hi páxai        kaopáp.i.sai.xáagahá
 H.        he fish-species catch.EPEN.NOMIN.certainty

Interestingly, Pirahã uses five discourse channels; information may be spoken (the default), whistled, hummed, yelled or encoded in music. Whistled languages are rare, making Pirahã an interesting study in the strength of tone and stress in communication.

Pirahã has a few loan words, mainly from Portuguese. Pirahã kóópo cup is from the Portuguese word copo, and bikagogia business comes from Portuguese mercadoria.

Only about 150 people speak Pirahã, in eight villages along the Maici; however, most of these people are monolingual, knowing only a few words of Portuguese. It is the belief of the Pirahã people that their language is the best one to speak, so there seems to be no immediate danger of Pirahã dying out.