It is common in contemporary clinical practice to be able to keep a person's body alive after the functions of the brain which animate and give character to that life have been irreversibly destroyed. In many countries there are brain stem death tests which allow us to come to a reliable clinical decision that the brain function required to sustain and animate the body has been lost. The nature of these tests are a matter of clinical neuroscience but the significance of brain death concerns our concept of the person and the value of human life.