Mapudungu(n), sometimes also called Mapuche or Araucanian, is not only one of the indigenous languages of the Americas whose genetic affiliation is still obscure but also one of the comparatively few languages of the region spoken by a considerable number of speakers (some thousands in Argentina and an uncertain figure -possibly close to 200'000 native, but not monolingual, speakers- in South Central Chile). Mapudungun has been rightly recognized as a crucial factor in this ethnic group's struggle for cultural survival. Despite the fact that the bulk of indigenous loanwords in Chilean and Argentinian Spanish comes from other languages, especially Chilean toponymy shows a profound Mapudungun influence way beyond present-day Mapuche territories. Although there are some more or less comprehensive grammars of the language written in the 20th century, this is to be the first short reference grammar of this polysynthetic language available in English. Some remarkable features are the following: rather simple phonology (unlike its surviving neighbors, Mapudungun has neither uvular nor glottalized phonemes; there are six vowels and only few consonant clusters), simple nominal morphology (neither case nor gender, marginal number), fairly complex verbal morphology (detailed aspectual and spatial categories, several productive valency-changing operators, polypersonalism, inverse system, nominal incorporation), and clause linkage patterns that rely heavily on semantically rather vague reduced verb forms.