Taurine is one of the most abundant amino acids in the body, found in especially high concentrations in the heart, brain, and skeletal muscle, yet classified as conditionally essential because synthesis may be insufficient during periods of high demand. It plays key roles in bile acid conjugation, calcium signaling in heart muscle, neuroinhibitory activity, and antioxidant defense in tissues. Recent longevity research has identified taurine decline as a hallmark of aging, with supplementation extending lifespan in animal models. Athletes use it for hydration, endurance, and reducing exercise-induced muscle damage.