Antarctic biodiversity is much more extensive, ecologically diverse and biogeographically structured than previously thought. Understanding of how this diversity is distributed in marine and terrestrial systems, the mechanisms underlying its spatial variation, and the significance of the microbiota is growing rapidly. Broadly recognizable drivers of diversity variation include energy availability and historical refugia. The impacts of local human activities and global environmental change nonetheless pose challenges to current and future understanding of Antarctic biodiversity. Life in the Antarctic and the Southern Ocean is surprisingly rich, and as much at risk from environmental change as it is elsewhere.The past two decades have witnessed a revolution in the approaches used to document patterns in and the functional significance of the diversity of life. Knowledge of the global distributions of organisms now extends to many groups. These include terrestrial plants and animals 1 , marine taxa 2 , components of the soil biota 3 , and, increasingly, microorganisms 4 .2 Empirical and theoretical research is verifying the range of mechanisms, including energy and nutrient availability, and historical contingency, that are responsible for these patterns 1,2 , and the role of diversity in maintaining ecosystem services. New approaches are also revealing rapid changes in diversity across most ecosystems, their often negative implications for the future of the planet, and our struggle to address the problem 5 .In tandem, biodiversity research has surged across the Antarctic and Southern Ocean.In part the increasing interest has been driven by the realization that any fundamental quest to understand life's diversity requires exploration of the polar regions 6,7 . But it has also been underpinned by a growing appreciation of the particular challenges faced by Antarctic species and ecosystems. Climate change 8 , and economic activity in the form of fishing, tourism, and scientific research itself 9,10 are all having impacts on Antarctic diversity. The intricacy of Southern Ocean food webs, best known for the region's iconic seals, penguins, whales and albatrosses, has been further unveiled, so highlighting the complexity of the simultaneous impacts of changing climates, sea ice distribution and fisheries on this system 11,12 . New marine research has also exposed unexpectedly high benthic diversity, including in the deep sea 13,14 . In terrestrial areas, the diversity of higher plants and animals is relatively low (e.g., just two flowering plant species), but the diversity of lichens, bryophytes, invertebrates, and the microbiota is substantial 15 . Local and regional spatial patterning in these groups is extensive 16 , with the mechanisms underlying these patterns both recognizable from broader ecological theory and unusual in several respects.Here we explore recent advances in our understanding of the biodiversity of the Antarctic. Given the many conservation challenges it faces, we also consider how well the region i...