Aboriginal Australians are the various Indigenous peoples of the Australian mainland and many of its islands, excluding the ethnically distinct people of the Torres Strait Islands.

Humans first migrated to Australia at least 65,000 years ago, and over time formed as many as 500 language-based groups. In the past, Aboriginal people lived over large sections of the continental shelf. They were isolated on many of the smaller offshore islands and Tasmania when the land was inundated at the start of the Holocene inter-glacial period, about 11,700 years ago. Despite this, Aboriginal people maintained extensive networks within the continent and certain groups maintained relationships with Torres Strait Islanders and the Makassar people of modern-day Indonesia.

Aboriginal Australians have a wide variety of cultural practices and beliefs that make up the oldest continuous cultures in the world. At the time of European colonisation of Australia, the Aboriginal people consisted of complex cultural societies with more than 250 languages and varying degrees of technology and settlements. Languages (or dialects) and language-associated groups of people are connected with stretches of territory known as "Country", with which they have a profound spiritual connection. Over the millennia, Aboriginal people developed complex trade networks, inter-cultural relationships, law and religions.

Contemporary Aboriginal beliefs are a complex mixture, varying by region and individual across the continent. They are shaped by traditional beliefs, the disruption of colonisation, religions brought to the continent by Europeans, and contemporary issues. Traditional cultural beliefs are passed down and shared through dancing, stories, songlines, and art that collectively weave an ontology of modern daily life and ancient creation known as the Dreaming.

Studies of Aboriginal groups' genetic makeup are ongoing, but evidence suggests that they have genetic inheritance from ancient Asian but not more modern peoples. They share some similarities with Papuans, but have been isolated from Southeast Asia for a very long time. They have a broadly shared, complex genetic history, but only in the last 200 years were they defined by others as, and started to self-identify as, a single group. Aboriginal identity has changed over time and place, with family lineage, self-identification, and community acceptance all of varying importance.

In the 2021 census, Indigenous Australians comprised 3.8% of Australia's population. Most Aboriginal people today speak English and live in cities. Some may use Aboriginal phrases and words in Australian Aboriginal English (which also has a tangible influence of Aboriginal languages in the phonology and grammatical structure). Many but not all also speak the various traditional languages of their clans and peoples. Aboriginal people, along with Torres Strait Islander people, have a number of severe health and economic deprivations in comparison with the wider Australian community.

Genetic studies have revealed that Aboriginal Australians largely descended from an Eastern Eurasian population wave during the Initial Upper Paleolithic. They are most closely related to other Oceanians, such as Melanesians. The Aboriginal Australians also show affinity to other Australasian populations, such as Negritos, as well as to East Asian peoples. Phylogenetic data suggests that an early initial eastern lineage (ENA) trifurcated somewhere in South Asia, and gave rise to Australasians (Oceanians), Ancient Ancestral South Indian (AASI), Andamanese and the East/Southeast Asian lineage, including ancestors of the Native Americans. Papuans may have received approximately 2% of their geneflow from an earlier group (xOOA) as well, next to additional archaic admixture in the Sahul region.

Aboriginal people are genetically most similar to the indigenous populations of Papua New Guinea, and more distantly related to groups from East Indonesia. They are more distinct from the indigenous populations of Borneo and Malaysia, sharing drift with them than compared to the groups from Papua New Guinea and Indonesia. This indicates that populations in Australia were isolated for a long time from the rest of Southeast Asia. They remained untouched by migrations and population expansions into that area, which can be explained by the Wallace line.

In a 2001 study, blood samples were collected from some Warlpiri people in the Northern Territory to study their genetic makeup (which is not representative of all Aboriginal peoples in Australia). The study concluded that the Warlpiri are descended from ancient Asians whose DNA is still somewhat present in Southeastern Asian groups, although greatly diminished. The Warlpiri DNA lacks certain information found in modern Asian genomes, and carries information not found in other genomes. This reinforces the idea of ancient Aboriginal isolation.

Genetic data extracted in 2011 by Morten Rasmussen et al., who took a DNA sample from an early-20th-century lock of an Aboriginal person's hair, found that the Aboriginal ancestors probably migrated through South Asia and Maritime Southeast Asia, into Australia, where they stayed. As a result, outside of Africa, the Aboriginal peoples have occupied the same territory continuously longer than any other human populations. These findings suggest that modern Aboriginal Australians are the direct descendants of the eastern wave, who left Africa up to 75,000 years ago. This finding is compatible with earlier archaeological finds of human remains near Lake Mungo that date to approximately 40,000 years ago. The idea of the "oldest continuous culture" is based on the Aboriginal peoples' geographical isolation, with little or no interaction with outside cultures before some contact with Makassan fishermen and Dutch explorers up to 500 years ago.

The Rasmussen study also found evidence that Aboriginal peoples carry some genes associated with the Denisovans (a species of human related to but distinct from Neanderthals) of Asia; the study suggests that there is an increase in allele sharing between the Denisovan and Aboriginal Australian genomes, compared to other Eurasians or Africans. Examining DNA from a finger bone excavated in Siberia, researchers concluded that the Denisovans migrated from Siberia to tropical parts of Asia and that they interbred with modern humans in Southeast Asia 44,000 years BP, before Australia separated from New Guinea approximately 11,700 years BP. They contributed DNA to Aboriginal Australians and to present-day New Guineans and an indigenous tribe in the Philippines known as Mamanwa. This study confirms Aboriginal Australians as one of the oldest living populations in the world. They are possibly the oldest outside Africa, and they may have the oldest continuous culture on the planet.

A 2016 study at the University of Cambridge suggests that it was about 50,000 years ago that these peoples reached Sahul (the supercontinent consisting of present-day Australia and its islands and New Guinea). The sea levels rose and isolated Australia about 10,000 years ago, but Aboriginal Australians and Papuans diverged from each other genetically earlier, about 37,000 years BP, possibly because the remaining land bridge was impassable. This isolation makes the Aboriginal people the world's oldest culture. The study also found evidence of an unknown hominin group, distantly related to Denisovans, with whom the Aboriginal and Papuan ancestors must have interbred, leaving a trace of about 4% in most Aboriginal Australians' genome. There is, however, increased genetic diversity among Aboriginal Australians based on geographical distribution.

Carlhoff et al. 2021 analysed a Holocene hunter-gatherer sample ("Leang Panninge") from South Sulawesi, which shares high amounts of genetic drift with Aboriginal Australians and Papuans. This suggests that a population split from the common ancestor of Aboriginal Australians and Papuans. The sample also shows genetic affinity with East Asians and the Andamanese people of South Asia. The authors note that this hunter-gatherer sample can be modelled with ~50% Papuan-related ancestry and either with ~50% East Asian or Andamanese Onge ancestry, highlighting the deep split between Leang Panninge and Aboriginal/Papuans.

Mallick et al. 2016 and Mark Lipson et al. 2017 study found the bifurcation of Eastern Eurasians and Western Eurasians dates to least 45,000 years ago, with indigenous Australians nested inside the Eastern Eurasian clade.

Two genetic studies by Larena et al. 2021 found that Philippines Negrito people split from the common ancestor of Aboriginal Australians and Papuans before the latter two diverged from each other, but after their common ancestor diverged from the ancestor of East Asian peoples.

The dingo reached Australia about 4,000 years ago. Near that time, there were changes in language (with the Pama-Nyungan language family spreading over most of the mainland), and in stone tool technology. Smaller tools were used. Human contact has thus been inferred, and genetic data of two kinds have been proposed to support a gene flow from India to Australia: firstly, signs of South Asian components in Aboriginal Australian genomes, reported on the basis of genome-wide SNP data; and secondly, the existence of a Y chromosome (male) lineage, designated haplogroup C∗, with the most recent common ancestor about 5,000 years ago.

The first type of evidence comes from a 2013 study by the Max Planck Institute for Evolutionary Anthropology using large-scale genotyping data from a pool of Aboriginal Australians, New Guineans, island Southeast Asians, and Indians. It found that the New Guinea and Mamanwa (Philippines area) groups diverged from the Aboriginal about 36,000 years ago (there is supporting evidence that these populations are descended from migrants taking an early "southern route" out of Africa, before other groups in the area). Also the Indian and Australian populations mixed long before European contact, with this gene flow occurring during the Holocene (c. 4,200 years ago). The researchers had two theories for this: either some Indians had contact with people in Indonesia who eventually transferred those Indian genes to Aboriginal Australians, or a group of Indians migrated from India to Australia and intermingled with the locals directly.

However, a 2016 study in Current Biology by Anders Bergström et al. excluded the Y chromosome as providing evidence for recent gene flow from India into Australia. The study authors sequenced 13 Aboriginal Australian Y chromosomes using recent advances in gene sequencing technology. They investigated their divergence times from Y chromosomes in other continents, including comparing the haplogroup C chromosomes. They found a divergence time of about 54,100 years between the Sahul C chromosome and its closest relative C5, as well as about 54,300 years between haplogroups K*/M and their closest haplogroups R and Q. The deep divergence time of 50,000-plus years with the South Asian chromosome and "the fact that the Aboriginal Australian Cs share a more recent common ancestor with Papuan Cs" excludes any recent genetic contact.

The 2016 study's authors concluded that, although this does not disprove the presence of any Holocene gene flow or non-genetic influences from South Asia at that time, and the appearance of the dingo does provide strong evidence for external contacts, the evidence overall is consistent with a complete lack of gene flow, and points to indigenous origins for the technological and linguistic changes. They attributed the disparity between their results and previous findings to improvements in technology; none of the other studies had utilised complete Y chromosome sequencing, which has the highest precision. For example, use of a ten Y STRs method has been shown to massively underestimate divergence times. Gene flow across the island-dotted 150-kilometre-wide (93 mi) Torres Strait, is both geographically plausible and demonstrated by the data, although at this point it could not be determined from this study when within the last 10,000 years it may have occurred—newer analytical techniques have the potential to address such questions.

Bergstrom's 2018 doctoral thesis looking at the population of Sahul suggests that other than relatively recent admixture, the populations of the region appear to have been genetically independent from the rest of the world since their divergence about 50,000 years ago. He writes "There is no evidence for South Asian gene flow to Australia .... Despite Sahul being a single connected landmass until [8,000 years ago], different groups across Australia are nearly equally related to Papuans, and vice versa, and the two appear to have separated genetically already [about 30,000 years ago]."

Aboriginal Australians possess inherited abilities to adapt to a wide range of environmental temperatures in various ways. A study in 1958 comparing cold adaptation in the desert-dwelling Pitjantjatjara people compared with a group of European people showed that the cooling adaptation of the Aboriginal group differed from that of the white people, and that they were able to sleep more soundly through a cold desert night. A 2014 Cambridge University study found that a beneficial mutation in two genes which regulate thyroxine, a hormone involved in regulating body metabolism, helps to regulate body temperature in response to fever. The effect of this is that the desert people are able to have a higher body temperature without accelerating the activity of the whole of the body, which can be especially detrimental in childhood diseases. This helps protect people to survive the side-effects of infection.

Aboriginal people have lived for tens of thousands of years on the continent of Australia, through its various changes in landmass. The area within Australia's borders today includes the islands of Tasmania, K'gari (previously Fraser Island), Hinchinbrook Island, the Tiwi Islands, Kangaroo Island and Groote Eylandt. Indigenous people of the Torres Strait Islands, however, are not Aboriginal.

Census counts and intercensal change,
Aboriginal and Torres Strait Islander persons, 2006–2021

Census	Number of persons	Intercensal change (number)	Intercensal change (percentage)
2006	455,028	45,025	11.0
2011	548,368	93,340	20.5
2016	649,171	100,803	18.4
2021	812,728	163,557	25.2

In the 2021 census, people who self-identified on the census form as being of Aboriginal and/or Torres Strait Islander origin totalled 812,728 out of a total of 25,422,788 Australians, equating to 3.2% of Australia's population and an increase of 163,557 people, or 25.2%, since the previous census in 2016. Reasons for the increase were broadly as follows:

• Demographic factors – births, deaths and migration – accounted for 43.5% of the increase (71,086 people). In turn, 76.2% of that increase was attributed to people aged 0–19 years in 2021, broken down as 52.5% for 0–4 year olds (births since 2016) and 23.7% for 5–19 year olds.
• Non-demographic factors, which are complex to quantify, include persons identifying as Aboriginal and/or Torres Strait Islander in a particular census, and changes in census coverage and response – such as persons completing a census form in 2021 but not in 2016. These factors accounted for 56.5% of the increase in the Aboriginal and/or Torres Strait Islander population (92,471 people). The increase was higher than observed between 2011–2016 (39.0%) and 2006–2011 (38.7%).

Most Aboriginal people speak English, with Aboriginal phrases and words being added to create Australian Aboriginal English (which also has a tangible influence of Aboriginal languages in the phonology and grammatical structure). Some Aboriginal people, especially those living in remote areas, are multi-lingual. Many of the original 250–400 Aboriginal languages (more than 250 languages and about 800 dialectal varieties on the continent) are endangered or extinct, although some efforts are being made at language revival for some. As of 2016, only 13 traditional Indigenous languages were still being acquired by children, and about another 100 spoken by older generations only.