This chapter provides an overview of the legal and medical principles that underpin medical negligence litigation, including the definition of medical negligence, what constitutes a psychiatric injury, the psychiatric evaluation and practical issues which commonly arise, when undertaking a psychiatric assessment in the context of clinical negligence litigation. After criminal negligence, the elements of civil negligence are set out including duty of care and standard of care. Legal concepts of causation and psychiatric injury differ from medical or scientific causation. The professional obligations on the forensic psychiatry as expert are to be neutral and objective, to obtain and document consent, to structure how instructions are taken and how reports are written in the light of court guidelines. As with all areas of medicine, the expert must comply with the ethical, professional and legal obligations of doctors. Patient privacy and confidentiality of personal health information must be protected. Most, if not all, patients referred by their solicitors, or by the defendant medical indemnity body, will already feel betrayed and let down by the medical profession. They will be fearful and distrustful. On the other side, there is a clinician who fears reputational damage.