Informality, once associated with poor squatter settlements, is now seen as a generalised mode of metropolitan urbanisation. The chapter identifies the gaps in urban planning systems in selected African countries, focusing on Nigeria for the empirical survey. The study was based on a literature review from other African countries but used information from Ogun State as empirical support, with 227 houses selected using a random sampling technique. The findings reveal a significant relationship between planning approval and the socio-economic characteristics of the residents. The chapter argues that a weak urban planning system is one of the contributing factors to informality in African cities. Legal/institutional and political ideology frameworks for urban planning are the major causes of the weak urban planning system; but political will and interest also shape urban planning in Nigeria. The chapter calls for urban planning not only to be carried out within the legal and institutional framework in African cities; the diverse socio-economic characteristics of the residents and jurisdictional partitioning at the local level should also be considered.