Where decisions concerning children are made, the mantra of the decision needing to be made in the child’s best interest is familiar and seems unobjectionable. After all, children as potentially vulnerable members of our society surely deserve the highest levels of protection such a standard suggests? Closer inspection, however, reveals significant problems with the definition and application of such a term in practice. While these are common to all areas of decision-making concerning children, this book is focused upon the healthcare context. Here some of the most difficult and sensitive problems arise, concerning as they do the extent to which a child’s body can be examined and operated upon or affected by medicines, devices and procedures that are intended to bring about physiological or psychological change. Healthcare decisions made in childhood may have a significant impact upon the experiences and opportunities children will have both now and in the future and, in some cases, it is not only their physical and mental health but also their lives that are at stake.