Australia's heathlands are characterised by evergreen shrubs mostly < 2 m tall, with evergreen subshrubs, forbs and graminoids also conspicuous. They occur over a wide range of rainfall/temperature regimes that surround the semi-arid core of Australia, but are best represented under Mediterranean-type climates. Environmental constraints include nutrient-impoverished soils (low concentrations and/or skeletal), hydrological gradients over the landscape often accompanied by strong seasonal drought, and intense recurrent fires. Their evolutionary history can be traced back 100 million years when rainforest clothed much of Australia with local refugia not unlike those conducive to the formation of heaths today. Leaves are typically small, sclerophyllous, long-lived, and highly modified to reduce water loss and heat loads and store nutrients. The heathlands are renowned for their high species diversity at fine scales, landscape turnover and local endemism, with the Proteaceae, Myrtaceae, Fabaceae, Ericaceae, Restionaceae and Cyperaceae accounting for > 50% of biomass and species richness at any site. Most plant species resprout after fire, with some species showing pyrogenic flowering. Most seeds are of limited dispersability, including ant-dispersal, and are either stored in the soil or on the plant and require fire to stimulate their germination or release. Almost all species possess specialised modes of nutrition, especially mycorrhizas and clustered roots. Recent research has focused on understanding mechanisms that explain the high levels of species coexistence: these can be grouped into 11 hypotheses, with the most promising based on small growth forms, large regional species pools and stabilising processes (resource-partitioning) associated with rarity. Land clearing, weed invasion and root pathogens threaten the conservation of Australia's world-heritage heathlands.