The planning and development of cities and their expanding regions is a complex task, without adding a changing environment to the mix. Urbanisation has reached unprecedented levels with over 60 per cent of the global population living in cities. Importantly most of the megacities will be in the global south. Less understood is that the United Nations has identified that close to half of the world’s urban dwellers reside in relatively small settlements of less than 500,000 inhabitants, ‘while only around one in eight live in the 28 mega-cities with more than 10 million inhabitants’. The urban context will therefore be a shift to an urbanising global south characterised by an increasing number of mega cities, a declining rural population and many people still living in smaller settlements. Collectively our urbanising world will place enormous pressures on our global environmental systems. This presentation argues that the concept of ‘planetary boundaries’ in defining a ‘safe operating space’ provides an overarching global framework for guiding urban development in terms of monitoring aggregate impacts on the global environment. In essence, the planetary boundaries approach embodies the ‘think global, act local’ dictum. ‘Planning within planetary boundaries’ will therefore be a highly valuable future context for land use planners to better understand the impacts of urban systems on the global environment and the scale of urban adaptation necessary to build a long term sustainable future.