This chapter outlines key urban challenges facing communities and the urban environment in the twenty-first century. Ten cities already exceed urban populations of 20 million or more people in their greater urban areas (Tokyo, Jakarta, Seoul, Karachi, Shanghai, Manila, Delhi, Beijing, Guangzhou and Mumbai). The challenges of the urban twenty-first century are enormous: the scale and rate of urban growth, the impacts of climate change on cities and human settlements, the continuing levels of poverty and refugees and the demands on water and energy to service our growing cities. A series of UN Habitat Conferences, I, II and III, has culminated in a New Urban Agenda adopted by the United Nations, October 2016. The New Urban Agenda UN Habitat identifies the need for more integrated urban planning and management to respond to these complex challenges. Urban mobility, good governance and the ‘right to the city’ on access and equity considerations are major considerations. Embedding environmental and climate change considerations into urban strategies, plans and policies is critical. National urban policies are seen as crucial to implementation of all these agreements. Sustainable development strategies, supported by appropriate institutional mechanisms that can coordinate the range of stakeholder interests, are essential to provide the important link between global and local action. Whereas national strategies and overseas aid are key levers for implementation, much of the action occurs at the subnational and local level. This is where the growth of city networks has become invaluable. The development of global city networks to share knowledge and expertise is a real twenty-first-century reflection of cities. The chapter concludes that sustainable and resilient urban developments, human rights and civic engagement and action on climate change are fundamental to developing more sustainable solutions for our cities and regions.