The primary goal of the built environment is to create the infrastructure that facilitates the needs of the people that use them and elevate their quality of life. Sustainable development has encouraged architects and urban planners to be more sensitive toward the built environment’s economic, environmental, and social dimensions. Digital tools for performance assessment are commonly used to shorten the feedback loop in testing designs for buildings and neighbourhoods. However, these tools do not extend to the social dimension in the same way as the economic and environmental dimensions. This thesis aims to contribute to USS research and bridge the gap between theory and practice through digitalisation. It investigates USS in general and explores how it can be conceptualised and made operational to support architects and urban planners in their design process. The focus is on digital tools and how they can be integrated into the current architectural and urban design process. Two studies are carried out (A and B). Based on systematic literature analysis, study A explores the theoretical background of USS. It investigates the reasons for the lack of consensus on USS’s conceptualisation and how digital tools can be developed around these issues. Study B explores the development of an indicator to support practitioners in evaluating the ability of residents to achieve their daily needs and uses interviews with practitioners for feedback on the indicator and how it can be improved. The findings indicate that USS is a complex and often "fuzzy" topic. There are many definitions for USS but little consensus among them. By viewing USS as an empty signifier, stakeholders can collaboratively decide what social themes are important to them. Two categories of social themes are identified - social equity and social capital. Focusing on social and spatial equity, a USS indicator called Trip Completion Rate is developed and used to explore the ability of residents to fulfil their daily needs through examples. The interviews with practitioners suggest that an indicator for evaluating social issues is appreciated, but further development is required in communicating complex results to stakeholders. In conclusion, the findings of this thesis contribute to a better understanding of USS and how to operationalise it for architects and urban planners through indicators. To further advance the integration of USS into the design process of neighbourhoods, digital tools must focus on enhancing social equity in the built environment. Finally, it identifies the indicators, methods and future pathways to advance the design of socially sustainable neighbourhoods through digitalisation.