Planning support systems (PSS), as geo-information technology instruments, have been developed to support planning as urban planning is becoming highly complex. Recent advances in new information and communication technologies (ICTs) in the context of smart cities have provided new potentials to enrich PSS-support functions, but they do not constitute a "silver bullet;" in fact, PSS's potential roles in practice are impeded by fundamental and structural factors. This article argues that the evolving perceptions of planning together with the changing roles of PSS in supporting planning provide the foundations for solving these structural restrictions. It presents a genealogical exploration of planning thoughts and associated PSS supports over the past 70 years, which is cross-checked by the results of expert interviews. The analysis indicates that for a factual planning supportive role: (1) the focus on the urban planning issue at hand should be strengthened, since it determines the planning mode and the relevant PSS choice; (2) there is a need for a user-centered, demand-induced approach toward PSS developments in planning, aimed at better serving the real needs of PSS users and planning practices; and (3) and there is also a need for more sensitivity toward contextual factors in PSS developments and applications, since the specific contextual characteristics help to identify the complexity faced by planners and influence the relevant planning rationality and specific PSS to be applied. This article thus highlights the importance of considering planning support as a socio-technical innovation shaped through challenges in urban contexts and the relevant planning approaches applied to handle these challenges. Further recommendations are proposed for PSS developments and applications in future planning practice.