The concept of when human death occurs had for most of history been determined by criteria for cardiac death, defined as the cessation of a heartbeat and respiration. However, in the mid-1900's, a new definition of death emerged in the form of brain death, characterized by an irreversible cessation of brain and brainstem function. This definition was needed after resuscitation of the heart was made possible and a growing number of patients were in a state of ventilatory support but had undetectable brain function. The success of organ transplantation and the growing need for more organ procurements further reinforced the advantage of using neurological criteria to declare death. These advancements in medicine have created a need for a definition of death other than cardiac death and have led to the acceptance of brain death, though it is still the subject of controversy. It has been attacked as a concept with weak scientific foundations and ethical justifications, since the brain itself is not well understood and the definition is used to the advantage of the organ donation system. Those in opposition to the use of neurological criteria to pronounce death argue that it is not always correctly detected and is conceptually incoherent. It would help to resolve this point of controversy if accurate methods to detect brain death were standardized for all physicians to use when declaring death, so that no declarations could be termed inaccurate or incomplete. The definition of brain death needs more rigorous and updated scientific backing in its ability to be detected if it is to be imposed upon individuals by law, as it is in the United States. It is also possible that new research and developments in medical treatments will make the current definition of death subject to change, and understanding the underlying problems of the current definition of brain death will help eliminate issues in a new definition of death.