The mitochondrion is a double-membrane-bound cell organelle, which is responsible for processing oxygen and converting food substances into energy. It is essential for cellular bioenergetics and consequently plays a significant role in aging related energy deterioration. Aging is a natural biological process, which occurs in all living organisms and is characterized by declining bioenergetics. A loss of mitochondrial activity and quality is also linked with the development of a variety of age-related diseases. Aging has a negative effect on the mitochondrial heath, as it creates imbalances in the main mitochondrial-regulated pathways. Mitochondrial dysfunction occurs when the mitochondrion fails to function properly as a result of another disease or condition. Secondary mitochondrial dysfunction may be caused by a variety of diseases including diabetes, muscular dystrophy, cancer, Alzheimer's disease, and Lou Gehrig's disease. This book provides significant information to help develop a good understanding of the role of mitochondrion in aging and disease. It will serve as a reference to a broad spectrum of readers.