The different types of social connections that young people have when they grow up can affect their mental health. Yet we know very little about how these social factors interact with each other and how they impact the development of depression and anxiety in children and young people. We set out to study how, when and for whom social connections work as an active ingredient for the prevention of common mental health problems (depression and anxiety) in children and young people. We use data collected from ALSPAC to investigate how the development of depression and anxiety was impacted by different types of social connections at different stages of their life. We will use data collected about different types of social relationships experienced by the children and young people at different points in time (such as connections with their family, community, online, teachers and friends) to investigate how these affect development of depression and anxiety over time. We will also analyse data collected from respondents when they were children to see if there is evidence to suggest that social connections in early life affect the development of depression and anxiety at later time points.