This chapter examines human aging as a systemic consequence of declining mitochondrial function and the resulting cellular energy shortage. It quantifies the ATP demands of major cellular processes, showing how insufficient mitochondrial output drives epigenetic silencing, metabolic dysfunction, sleep disruption, fat accumulation, and the rise of senescent cells. The chapter then explores high‑volume mitochondrial transplantation as a potential intervention capable of restoring cellular energetics at scale, outlining requirements for stem‑cell sourcing, bioreactor expansion, mitochondrial extraction, and delivery. Finally, it considers the follow‑up therapies—senolytics, epigenetic reprogramming, stem‑cell replacement, and telomere restoration—that may be necessary to achieve full rejuvenation once mitochondrial energy supply is restored.