Why do we age? How does cancer develop? What is the connection between Alzheimer’s and heart attacks, or between infertility and hearing loss? What lies behind the term "weight loss paradox"? Can we extend our lifespan, and if so, how? Mitochondrial medicine provides the answers to all these questions. In his bestseller, Lee Know tells the story of mitochondria and sheds light on the long misunderstood and ignored powerhouses in our body’s cells. This story began over 2 billion years ago when one bacterium engulfed another without being destroyed. This fusion marked the birth of the first mitochondrion. Since then, all life that goes beyond the stage of a single-celled bacterium derives its energy from mitochondria. Understanding how mitochondria function is key.