Traditionally, mitochondria have been viewed as the "powerhouse" of the cell, i.e., the site of the oxidative phosphorylation machinery involved in ATP production. Consequently, much of the research conducted on mitochondria over the past 4 decades has focused on elucidating both those molecular events involved in ATP synthesis by oxidative phosphorylation and those involved in the biogenesis of the oxidative phosphorylation machinery. While monumental achievements have been made, and continue to be made, in the study of these remarkable but extremely complex processes essential for the life of most animal cells, it has been only in recent years that a large body of biological and biomedical scientists have come to recognize that mitochondria participate in other important processes. Two of these are cell death and aging which, not surprisingly, are related processes both involving, in part, the oxidative phosphorylation machinery. This new awareness has sparked a new and growing area of mitochondrial research, that has become of great interest to a wide variety of scientists ranging from those involved in elucidating the role of mitochondria in cell death and aging to those interested in either suppressing or facilitating these processes as it relates to identifying new therapies or drugs for human disease. It is the purpose of this brief introductory review to provide an overview of those mitochondrial events involved in the life and death of animal cells and to indicate how these events might relate to the human aging process. Much more is known, much remains controversial, and even more remains to be learned as indicated in the excellent set of minireviews that follow.