Abstract: Death is a phenomenon that resists simple explanation. While the cardiopulmonary criterion of death has been used for centuries, in most nations (including the US and Canada) brain death has also been accepted since 1968 as a second legal criterion, held to be biologically equivalent to bodily death. This equivalence has been argued to derive either from the brain’s control over body functions or from the brain’s work against entropy, with a dead brain thereby producing a dead body. Subsequently, some have found these claims wanting. An alternative body-centered view, based on the functioning of the body’s mitochondria, is that in brain death, only the brain is dead, while the body may not necessarily be. Mitochondria are cellular organelles descended from ancient bacteria, symbiotically providing energy for entropy-resistance and sharing control over life processes. All of death’s features – its universality, oxygen-dependence, inevitability, link with aging, irreversibility, and association with disintegration and decay – may be explained as logical side-effects of mitochondrial failure. Yet the role of mitochondria in human life and death has been overlooked for over four decades in the legal and bioethical literature, which has focused instead on processes at the whole-organism level. Challenges remain however: if brain death and bodily death are not biologically equivalent, this may prove problematic for organ donation’s “dead donor rule,” which requires organs to be transplanted only from the bodies of dead consenting donors, not from those who are still dying. Nevertheless, brain death could be retained as a legal fiction satisfying the dead donor rule, which would allow its societal benefits to persist. Of fundamental importance is the principle that future patients be adequately informed regarding brain death, in order to ensure legally valid, informed consent for organ donation.