Abstract: There have been few attempts to describe the key ecological relationships which may be controlling the biotic structure of the Australian arid zone. We develop a series of ‘propositions’ which state explicit models about the functioning of inland Australia, based on its special physical environment. These special features—an extremely unpredictable but only moderately arid climate, ancient and infertile soils, and a high degree of soil differentiation—are not unique to Australia, but are combined there over a majority of the arid zone, which makes up 70% of the continent. These features define a specific range of establishment and persistence opportunities for plants, with fertile or reliable sites scattered like islands in a sea of exceptionally infertile and unreliable conditions. However, unpredictable heavier rains result in a high diversity and persistence of perennial plants, which in turn support relatively stable populations of suitably adapted consumers. Mammalian herbivores are focused on small parts of the landscape, whereas detritivory and ectothermic predation dominate most areas to an extent not seen in other well-studied deserts of the world.