Sydney is increasingly oriented to compete in the global city stakes. This necessitates achieving higher rates of economic growth than rival cities, particularly in sectors such as international finance. Economic growth has spatial and resource dimensions that conflict with many visions of what constitutes a sustainable city. Sydney is Australia’s largest vortex city, sucking in resources for production and consumption and using other parts of the planet to assimilate wastes. This paper analyses the strengths and weaknesses of competing definitions and measuring techniques to identify sustainable cities, including Ecological Footprint Analysis, Taking Sustainable Cities Seriously and Sustainability Indicators. It applies these and other concepts to Sydney, thereby highlighting the critical choice of definition and measuring technique in debates about the sustainability of cities. The conclusion identifies the importance of communication, education and implementing appropriate processes to reduce the most unsustainable practices in Sydney, and in other Australian cities.