This article highlights the essential physiological roles of magnesium, a predominantly intracellular cation and critical cofactor in numerous enzymatic reactions that support metabolism, electrolyte balance, neuromuscular transmission, and muscle contraction. The majority of magnesium is stored in bone, with smaller amounts in muscle. Because 99% resides intracellularly, serum concentrations are a poor reflection of total body stores. Magnesium homeostasis is maintained through intestinal absorption, skeletal storage, and renal regulation. Hypomagnesemia can lead to refractory hypokalemia, hypocalcemia, tremors, and arrhythmias, though its nonspecific clinical signs are often masked by concurrent disorders. The article emphasizes the importance of accurate diagnosis, appropriate management, and supplementation.