Around 9% of UK adults have a serious mental illness such as schizophrenia, bipolar disorder, or a personality disorder (SMI or PD). People with these illnesses die earlier than the general population, and national data indicates that they often have fewer resources than they need to help keep them well. We know little about the housing in which most people with SMI and PD live. This is important because unsafe and unaffordable housing is associated with poor mental and physical health, and the UK is experiencing intense housing pressure in all sectors. In this project we will carry out preliminary work to help us assess the feasibility of conducting a national housing profile for people with SMI and PD. Together with a consortium of stakeholders we will review literature, map datasets that could contribute to the profile and understand how to measure housing insecurity in people with SMI and PD.