The urban design process must be transformed and improved if various stakeholders wish to create sustainable urban environments. Although the UK Government and other influential bodies have written many reports recently about the intimate relationship between urban design and sustainability, much more needs to be done to demonstrate how, when and where sustainability is embedded in the urban design process. There is also a need to understand who the decision makers are within this process and what influences their decisions. A clear picture of how the urban design decision-making process works from start to finish, and how sustainability is embedded within this process, can help to achieve the goals and objectives of urban sustainability in the 24-hour city. This paper begins by defining urban design and describing the urban design process, highlighting the major stages and the general tasks involved at each stage. Sustainability and urban sustainable development are briefly discussed next. The final section indicates, through case study research comprising the VivaCity2020 project, where sustainability may be embedded within the urban design process.