This collection of essays examines alternative theories about persons and personal identity at the beginning and end of life. The contributions seek to answer the important question, When does a person begin and cease to exist? While the concept of personhood has figured prominently in contemporary debates over abortion and stem cell research, this is the first anthology to combine in a single volume both various theoretical perspectives and consideration of the more practical, bioethical issues. These essays are gathered from a rich tradition of philosophical and religious readings on the subject, from Rene Descartes's Meditations on First Philosophy and John Locke's Essay concerning Human Understanding to more modern discussions on persons living with dementia and on the definition of death. Organized chronologically, these works address three broad topics: theories of persons, persons at the beginning of life, and persons at the end of life. The first section offers differing views on the nature of persons that have influenced ontological and bioethical discussions of the subject. Essays in the next section track the debate over abortion and the moral status of embryos. The last section explores alternative definitions and determinations of death. Defining the Beginning and End of Life is a useful resource for examining the connection between theoretical and bioethical considerations about persons. It will engage bioethicists and philosophers as well as inform policy and law regarding issues at the beginning and end of life.