This book is intended as an introduction to the complex and rapidly developing area of medical treatment and the law in relation to the vulnerable, namely children and those adults who lack capacity. It provides practical guidance and assistance as to the approach taken by the courts on all of the varying material issues raised in relation to medical treatment and the law, the thread of which throughout is the question of 'consent'. Care needs to be taken not to infringe the rights of that group of persons who, though vulnerable, are capable of making their own decisions. Many who suffer from mental illness are well able to make decisions about their medical treatment, and it is important not to make unjustified assumptions to the contrary. The substance of the book is intended, accordingly, to be of assistance not only to the legal profession and judiciary but also to those working within the field of medicine or other areas concerned with the welfare and protection of the vulnerable, whether adults or children. The text also includes analysis of The Supreme Court's judgment in the cases of Tony Nicklinson, Paul Lamb and AM [2014] UKSC 38 which encompasses the issues concerning assisted suicide, mercy killing and voluntary euthanasia. The general principles set out in Part I are elucidated upon in more detail in the remaining Parts II, III and IV of the book.