Abstract: Given the conspicuous and wide-ranging effects emanating from planning, this paper takes as its starting point the proposition that all planning, not least that directed at Australian cities, must address and resolve the issue of legitimacy in terms of what justifies its decision making and intervention(s). Specifically focusing on the discipline of social planning, with its complex relationships with that segment of the real world that we call ‘social reality’ or ‘social practice’, the paper argues that such planning must justify its legitimacy not only in terms of its actions and consequences, but, more significantly, on the basis of a substantive and critical examination of the values, knowledge, politics and ideologies that have underpinned its emergence throughout the 20 th century and that currently inform and drive it. Drawing on a much more substantive study currently being undertaken by the authors which examines the ways in which shifts in political ideology, changes in the acceptance and validation of different knowledge sources, and the growing awareness of the city as a living system of diverse forces which have been used to justify the presence of social planning throughout the 20 th and early 21 st centuries, the current paper briefly examines the history of the developing relations between urban planning and social expectations, and analyses the increasing acknowledgement of the importance of the social dimensions of cities within planning strategies.