Rapid urbanization, climate change, sustainable development, resource depletion, the widespread use of the Internet and mobile phones, and the big data phenomenon all pose great challenges to urban planning. By facilitating data exchange, collection, and analysis, technological innovation has already improved the planning process. However, planning methods, tools, and administrative organizations still lag behind in implementing change. Technological progress has certainly altered urban management by making it more efficient, producing smart cities where system-automation optimizes and regulates flows, as well as balances the use of resources. But what about city planning ? The citizens and infrastructures of smart cities produce a massive amount of data, which in turn calls for smart planning ; a more responsive kind of urban planning capable of integrating this valuable data from the field. Moreover, urban dwellers are often excluded from the planning process, even though they are the ones generating and experiencing the city. Understanding urban practices and dynamics is a necessary condition for sustainable urban planning. The data produced, both actively and passively, by citizens can help understand their habits and needs. The smart city model has already reached its limits. The complexity of issues, social and urban dynamics, multiple involved actors, and technological innovation are all elements which demand reexamination of data sharing, production, and analysis to better determine the roles of urban data and urban dwellers. A new city model is emerging : the responsive city, which places urbanites at the center of reactive urban development. This research aims to consider the system formed by these citizens, their city (urban planners), and the digital world. First, it intends to identify the role of citizens in urban planning processes through a detailed study of existing digital participation tools. Second, the two case study cities of Geneva and Singapore are used to understand the implications of technological development in urban planning practices. Particular attention is given to changes taking place under the impulse of digital technology. The overall issues, generated data, its uses and limitations, as well as the promises of digital participation tools are all put into perspective through an integrated study of the cityâs development process. The study of digital participation tools, and the analysis and comparison of urban planning processes in Geneva and Singapore highlight changes in citiesâ production process which are necessary to meet contemporary urban challenges. The results show that planning tools are no longer valid, that the role of both urban planners and urban dwellers is changing rapidly, and finally, that, urban governance is moving towards more collaborative and reactive forms to maintain control over territorial development. This thesis explores the limits of current systems, examines the opportunities emerging with technological development, identifies the barriers and catalysts preventing or encouraging change, and makes recommendations for moving from the smart to the responsive city.