In the late 18th century, there were more than 250 distinct Aboriginal social groupings and a similar number of languages or varieties. At the start of the 21st century, fewer than 150 Aboriginal languages remain in daily use, and all except only 13, which are still being transmitted to children, are highly endangered. The surviving languages are located in the most isolated areas. Of the five least endangered Western Australian Aboriginal languages, four belong to the Ngaanyatjarra grouping of the Central and Great Victoria Desert. Yolŋu languages from north-east Arnhem Land are also currently learned by children. Bilingual education is being used successfully in some communities. Seven of the most widely spoken Australian languages, such as Warlpiri, Murrinh-patha and Tiwi, retain between 1,000 and 3,000 speakers. Some Aboriginal communities and linguists show support for learning programmes either for language revival proper or for only "post-vernacular maintenance" (teaching Indigenous Australians some words and concepts related to the lost language).
Whether it is due to genetic unity or some other factor such as occasional contact, typologically the Australian languages form a language area or Sprachbund, sharing much of their vocabulary and many distinctive phonological features across the entire continent.
A common feature of many Australian languages is that they display so-called avoidance speech, special speech registers used only in the presence of certain close relatives. These registers share the phonology and grammar of the standard language, but the lexicon is different and usually very restricted. There are also commonly speech taboos during extended periods of mourning or initiation that have led to numerous Aboriginal sign languages.
For morphosyntactic alignment, many Australian languages have ergative–absolutive case systems. These are typically split systems; a widespread pattern is for pronouns (or first and second persons) to have nominative–accusative case marking and for third person to be ergative–absolutive, though splits between animate and inanimate are also found. In some languages the persons in between the accusative and ergative inflections (such as second person, or third-person human) may be tripartite: that is, marked overtly as either ergative or accusative in transitive clauses, but not marked as either in intransitive clauses. There are also a few languages which employ only nominative–accusative case marking.
A typical Australian phonological inventory includes just three vowels, usually , which may occur in both long and short variants. In a few cases the has been unrounded to give .