To know whether eco-cities or, indeed, any so-called sustainable urban environment, will be successful, an understanding is needed about how such places 'come into being'. Understanding how decisions have been made, who makes them and when and how they are made is crucial to ensuring that the 'right' people have been involved at 'right' time. In describing and visualizing this, we are providing a framework-in this case, an urban design decision-making process-that highlights the stakeholders as well as the tensions, tradeoffs and decisions that need to be made in the name of shaping sustainable developments. This paper presents the findings from a large-scale research project about sustainable urban design decision-making and the 24-hour city. Through in-depth, case study research in three UK cities, the work identified and visualized a new framework for the urban design decision-making process as well as making crucial connections to urban form, the urban experience and urban policy. The project is described, highlighting the multi-disciplinary team approach and the diverse areas explored within the project. The three case study cities are then discussed briefly, followed by some of the distinct, area-focused results as well as some the integrated findings. In particular, the improved urban design process will be explained along with a description of some of the tools and techniques developed for urban design decision-makers.