 The philosophical investigation of human death has focused on two overarching questions: (1) What is human death? and (2) How can we determine that it has occurred? The first question is ontological or conceptual. An answer to this question will consist of a definition (or conceptualization). Examples include death as the irreversible cessation of organismic functioning and human death as the irreversible loss of personhood. The second question is epistemological. A complete answer to this question will furnish both a general standard (or criterion) for determining that death has occurred and specific clinical tests to show whether the standard has been met in a given case. Examples of standards for human death are the traditional cardiopulmonary standard and the whole-brain standard. Insofar as clinical tests are primarily a medical concern, the present entry will address them only in passing.