The urban contexts in which planning occurs differ significantly from one region to another. This chapter examines the nature of these differences, focusing on the consequent challenges that urban planning should address. As briefly indicated in Chapter 1 and elaborated upon in Chapter 3, the view of urban problems as being essentially uniform across the world partly underlies efforts to create universal urban planning approaches and models. Evidence in this Global Report suggests that this view is flawed and partly accounts for the failure of urban planning in many countries. The underlying premise of this chapter is that urban planning initiatives are unlikely to succeed without an adequate understanding of the diversity of urban contexts. Collectively, demographic, size, spatial and economic factors, mediated by globalization and location, are of paramount importance in revisiting urban planning and determining the ways in which it should be reoriented and strengthened in order to make it more relevant.