Total-body potassium (K+) content and appropriate distribution of K+ across the cell membrane is vitally important for normal cellular function. Total-body K+ content is determined by changes in excretion of K+ by the kidneys in response to intake levels. Under normal conditions, insulin and β-adrenergic tone also make important contributions in maintaining internal distribution of K+. However, despite these homeostatic pathways, disorders of altered K+ homeostasis are common. Appreciating the pathophysiology and regulatory influences that determine the internal distribution and external balance of K+ is critical in designing effective treatments to restore K+ homeostasis.