In the UK, more people who have psychosis live in cities than rural areas, and there is a large body of evidence suggesting that city living may be associated with a higher risk of psychosis. However, the reasons underlying this remain poorly understood. Although it has been suggested that city living may be associated with a heightened risk of social isolation, being ‘less connected’ to others resident in local communities, and/ or living in more deprived areas which are known to be associated with poor mental health, evidence relating to this remains scarce, particularly from the UK. Public Health England and other local government bodies are increasingly interested in supporting policies targeted at making cities more mental-health friendly, yet data to support such policy remains scarce. In this project we will use electronic health records from one of the largest secondary mental health providers in Europe, covering a catchment of 1.3 million people resident in a well-defined catchment area across the London boroughs of Southwark, Lambeth, Lewisham and Croydon, linked to individual-level information from UK census 2011 (a rich source of information on individual social contexts), to assess the risk of city living being associated with psychosis. The linked dataset comprises around 20,000 people with psychosis each matched to five people without mental health problems, who will act as a ‘control’ or comparison group. This dataset will enable a quantitative assessment of predictors in the urban built environment (including household poverty, social isolation, family support, ethnicity/ migration status) with the onset of psychosis, in a way that has not been previously possible in the UK. The student undertaking this PhD will also interview up to 20 people with psychosis, to understand their experiences of city living and mental health problems. The information from these interviews will be combined with the quantitative findings from the health records, to further inform insights. The CASE partners for this project, The Centre for Mental Health, is a charity with a major focus on tackling mental health inequalities. Together with the Centre for Mental Health, areas of this project relevant to urban policy will be mapped, taking into account the views of relevant stakeholders (for example public health and charities), which will ensure that findings are translated into actionable policy recommendations.