Under physiologic conditions, the acid-base balance of the body is maintained via changes in ventilation that eliminate carbon dioxide, buffering of acid loads, and renal excretion of hydrogen ions. Failure to maintain the pH of the blood between 7.35 and 7.45 can result in life-threatening conditions. This review details the pathophysiology, stabilization and assessment, diagnosis and treatment, and disposition and outcomes of acid-base disorders. Figures show the relationship between hydrogen ions and blood pH, proximal tubular bicarbonate reabsorption, the secretion of hydrogen ions, renal ammonia production, ammonium diffusion, metabolic alkalosis, electrocardiographic changes in hypokalemia and hyperkalemia, pseudoinfarction caused by hyperkalemia, and an algorithmic approach to suspected acid-base disorders. Tables list causes of high–anion gap metabolic acidosis, metabolic acidosis with a normal anion gap, type 1 renal tubular acidosis, type 4 renal tubular acidosis and aldosterone resistance, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis; treatment of hyperkalemia; and a stepwise approach for the evaluation of suspected acid-base disorders. This review contains 9 highly rendered figures, 9 tables, 64 references, and a list of pertinent Web sites.