This chapter serves as an introduction to the book and provides brief information about urbanization in West Africa, and in Ghana in particular, the general role of urban agriculture and the common use of polluted irrigation water. It describes our focus on irrigated smallholder vegetable production and our understanding of the terms 'urban', 'peri-urban' and 'wastewater'. The chapter reflects on some of the key challenges of the farming system, its dynamic and resilience. It also gives an overview on the structure of the book, the origins of the data and the main objective of this publication. 1.1 The Urbanization Challenge Globally, more people are living today in urban as opposed to rural areas. In West Africa, which hosts the megacity of Lagos, the population living in urban areas has increased from only 4% in 1920 to 45% in 2011. The 50% benchmark has been passed in Ghana as in the quickly urbanizing coastal belt of West Africa, while the drier and less populated northern belt of West Africa remains so far mostly rural. For Ghana, a population split of 50.9% urban to 49.1% rural (Table 1.1) has been estimated based on the 2010 census (GSS 2012c).