Urban growth and the increase of the human environmental imprint has led to a growing interest in urban sustainability, a field mainly addressed by urban ecology and urban metabolism studies. The realisation that the urban material and energy flows are mainly driven by household activities resulted in the acknowledgement that to understand the drivers of urban metabolic trajectories, it is necessary to include social factors into the onceptualisation of the urban system. However, so far no satisfying and operationalisable conceptualisation of the urban system as a nexus of social, technological, geographical and environmental factors exists. The aim of the present research is to develop an approach to overcome this gap. This research starts with the assumption that the household processes driving the urban material and energetic flows are key to understanding urban metabolic regimes and trajectories. It thus attemps to study urban transitions from a social practice theoretic approach. This methodological choice is motivated by the ambition of social practice theory to analyse the formation, reproduction and transformation of practices - nested sets of routinised activities - as parts of a system of things, technologies, skills, social structures, meanings, the environment etc., and in general by its focus on understanding the mechanisms behind social change. However, social practice theory has been struggling with the operationalisation of its concepts, due to the nestedness of practices and the resulting difficulty to delimit the field of analysis, and the lack of a general theory of how the different elements of which social practices consist are related. To overcome these challenges, this research proposes to model urban trajectories and transitions as the emergent behaviour of a socioechnological-environmental system, of which the different components drive the formation, reproduction andtransformation of social practices and thus the urban metabolic flows. For this, a mixed-method approach of agent-based and system dynamics modelling informed by sociological theories and qualitative field work is to be developed. Firstly, urban trajectories and patterns are identified. Secondly, models are used as a tool to test different theory-based explanatios for the emergence of such patterns. More specifically, the aim is to replicate long-term patterns and trajectories of specific practices - such as nutrition or commuting - across different urban contexts based on different theories regarding social change and the formation of social practices. The model hypotheses are to be developed based on theories and qualitative data, and tested with participatory approaches.