Mental health problems are very common – affecting around one in four people- they include many different commonly diagnosed forms such as depression, bipolar disorder and schizophrenia. How mental health problems develop is a complex issue and involves both life experiences, and variation in the DNA sequences that encode and regulate genes. Understanding which genes are affected will allow us to develop more effective treatments for mental illness and to begin to understand how events in people’s life trigger such illnesses. By examining the differences in DNA sequence between many hundreds or thousands of individuals, both affected and unaffected by mental health issues, we hope to use statistical methods to identify the relevant genes and explore their function to gain a better understanding of the processes disrupted in mental illness.