Current discussions of ‘mental health’ obscure the fact that there are many different recognised different disorders, not all preventable, and not all responsive to the same approaches. This chapter provides an overview of the nature of mental illness, signposting readers for information on specific conditions to chapters elsewhere in the book. It is not appropriate for lay people to diagnose, treat or case-manage a student’s or colleague’s mental illness. However, some background awareness of the nature of mental illnesses can inform helpful responses. Mental disorders bring implications for admissions policies, rights and responsibilities, fitness to study and to practice, information-sharing with parents, provision of services and links with NHS and third sector. ‘Disclosing’ a mental health condition to the university provides rights to support, services and finance – the DSA (disabled students allowance). The key to accessing all NHS treatment is to be signed on with a local GP, but currently General Practices are financed better for elderly caseloads. Networking with university in-house mental health services is essential . Arrangements to hold GP and Psychiatric clinics on University premises are particularly welcome.