Ideological rationalities and urban planning practices are inextricably linked, and urban planning practices draw insight from theoretical propositions. Through a review of relevant literature and documents, the chapter traces ideological changes and their influences on urban planning practices in colonial to post-colonial Tanzania. Colonial urban planning was based on modernist ideological rationalities drawing from layout planning, land use zoning and master planning. Post-colonial planning practices underwent changes in ideological rationalities from master planning to strategic planning. Master planning as modernist planning has always been an expert-led process based on means–ends and dualistic ideas. Strategic planning as post-modernist planning has been based on relations and pluralistic ideas. Non-implementation of master plans and strategic plans have rendered layout plans as the main spatial planning and decision-making tool. Contemporary planning realities are influenced by a multitude of challenges resulting in the emergence of piecemeal planning leading to uncoordinated urban forms, particularly in small towns.