Australia is one of the world's 17 megadiverse countries, and its long geographic isolation has led to the development of a vast array of unique species. Around 94% of Australia’s amphibians, 93% of its reptiles and flowering plants, 69% of its mammals, and 46% of its birds are endemic, making it a global biodiversity hotspot. The country’s vast range of ecosystems is divided into 89 regions and 419 subregions, each offering distinct habitats for its unique flora and fauna. As of January 2025, the Australian National Species List included 168,386 named species, with estimates suggesting that up to 70% of the country’s species remain undiscovered and unclassified, potentially numbering up to 600,000.

Australia boasts about 10% of the world’s known plant species, many of which are adapted to the arid conditions and nutrient-poor soils that cover much of the mainland. Desert ecosystems and xeric shrublands dominate about 70% of Australia’s land area. Iconic plant species such as acacia, banksia, and eucalyptus thrive in these harsh conditions, with many plants having developed tough, long-living leaves resistant to bushfires.

Australia is also home to around two-thirds of the world's marsupial species and roughly 10% of the world's reptile species. Invertebrates, particularly insects, make up the bulk of Australia's animal species, while fungi are similarly diverse, though much of Australia’s fungal life remains unclassified. Animals like the koala and honey possum have evolved to feed on nectar, pollen, and eucalyptus leaves, demonstrating the unique adaptations of Australian species to their environment. Additionally, the evolution of Australian marsupials shows similarities to placental mammals on other continents, suggesting convergent evolution in response to similar environmental pressures.

Despite its rich biodiversity, Australia faces ongoing challenges in wildlife conservation. Major extinctions, particularly of the country’s megafauna, occurred around 46,000 years ago, with human activity and climate change playing roles in these losses. Today, Australia has lost more mammal species than any other continent, and currently, 100 species are listed as extinct or extinct in the wild. In 2021, over 1,000 animal and plant species were classified as endangered or critically endangered, with threats including habitat disruption, the introduction of invasive species such as feral cats and foxes, and climate change.

Efforts to protect Australia's biodiversity are ongoing. The Environment Protection and Biodiversity Conservation Act 1999 serves as the primary legal framework for safeguarding threatened species. The National Reserve System, which as of 2022 covers over 22% of Australia’s land mass, plays a critical role in conservation. Additionally, Australia’s Strategy for Nature 2024–2030 aims to reverse biodiversity loss by 2030 and fulfill international commitments under the United Nations Convention on Biological Diversity.

The preservation of Australia's extraordinary biodiversity remains a critical challenge. Despite the country’s efforts, the threats facing its unique species are ever-present, requiring continued conservation efforts and policies that balance environmental protection with the needs of growing human populations.