The scientific literature on smart cities has focused on innovative developments in information and communication technology (ICT) and on its consequences for urban life and policy making. In line with these, Batty et al. (Eur Phys J Spec Top 214:481-518, 2012) state that new technological developments are providing for new types of analysis, public participation and multi-actor collaboration, blurring the boundaries between smart cities and urban planning. We take this statement as a starting point for our discussion and put attention on the interplay between new ICT, smart cities and spatial planning. We focus in particular on the triangular relationship between smart governance as one of the areas of smart cities (Giffinger et al. in Ranking of European medium-sized cities, 2007), collaborative planning as a present form of spatial planning, and planning support systems (PSS) as a specific form of ICT dedicated to planning tasks. Collaborative planning is characterized by consensus building among distinctive stakeholders in participatory processes. Smart governance adds ICT-related components (e.g. efficient communication; data exchange) to the concept of collaborative planning. Finally, PSS involves the creation and use of tools to support professional planners' tasks, including introducing relevant geoinformation and facilitating participation. To illustrate this triangular relationship, we examine some practical case studies from China, Finland, and the USA that suggest how web-based and model-based PSS can fulfil a supportive role, to realize smart governance in spatial planning by promoting effective communication and collaboration between various actors, and by strengthening the transparency of the decision-making process. We conclude that collaborative planning can become a form of smart governance under two basic conditions, namely of recent developments in the applicable ICT and an appropriate institutional design.