Including marine and fresh water fish, nearly 1200 species of native vertebrates occur or are reported to have occurred as wild or free-living animals within the Greater Sydney Region; an area of more than 2,500 km² encompassing both the most densely populated city in Australia and World Heritage Wilderness. Sydney Harbour alone has a fish fauna of nearly 600 species. Almost all of the free-living vertebrates found in the Region are native to Australia, with fewer than 40 species being introductions to the continent. To a considerable extent, the Region owes the biological richness of its native vertebrates to large expanses of native vegetation on the urban perimeter, with many fewer species maintaining breeding populations in the Region's urban, suburban and rural terrestrial habitats as commensals of human society. A large proportion of the latter, particularly among birds, are species exotic to the region or which originally occurred in small numbers and have benefited from Sydney's urbanization. However, the greatest vertebrate biological diversity in the Region's more developed areas is the vast array of exotic fish, reptiles, birds and mammals, including Australian species exotic to the Region, kept by people as companion animals, pets and working animals (e.g., racehorses, livestock, those in zoos and animal parks, laboratory rats) and their feral counterparts. These animals constitute by far the greatest diversity, if not abundance, of terrestrial vertebrates in the Sydney Region and interact significantly with the city's culture, ecology and economy. They also pose a continuing risk of establishing feral populations or acting as conduits of disease and pathogens into native wildlife suggesting a need for much better accounting and monitoring of their numbers than currently occurs. Together with the Region's indigenous flora and fauna, Sydney's exotic plants and animals create a ‘hot spot for biodiversity’ exceeding any natural area in its richness, with a total species richness of higher plants and vertebrates in excess of 10,000 species. Recognition of the importance of non-native animals (and plants) to urban society and ecosystems is overdue. Moreover, in an era of accelerating habitat loss, human population growth, urban expansion and climate change the role of cities in conserving global biodiversity may prove critical. Zoologists and conservation biologists already accept the role of zoos in international and national conservation efforts and it is time to accept the importance for conservation of all the other species held in captivity by people. We may be unwilling to accept companion animals and exotic species as ‘wildlife’, but we cannot deny their existence as part of the urban fauna nor their importance to urban lifestyles. Equally, the urban landscape can be important for the conservation of continental biodiversity by providing additional habitat for native animals and plants and by bringing city dwellers into contact with native species which they might not otherwise encounter or even be aware of. Thus, the conservation and management of an urban fauna is fundamentally different from that required outside the urban environment, with not only a far greater diversity of species to be responsible for, but one with very different cultural, educational and social objectives.