Several physiological mechanisms act to regulate renal potassium excretion and distribution. Together they comprise an integrated control system that may be envisioned as being made up of several interacting negative feedback control mechanisms, all affecting removal of potassium from the extracellular fluid by renal excretion or transfer across cell membranes into or out of the intracellular compartment. The intent of this presentation is to describe the mechanisms of potassium regulation, beginning in Chapter 1 with an overview of the system, Chapter 2 with mechanisms that determine movement of potassium between the extracellular and intracellular compartments, in Chapter 3 focusing on renal tubular transport systems, and in Chapter 4 presenting the mechanisms of control of aldosterone secretion. Greatest emphasis will be on describing the integrated functions of the components, in Chapter 5, as they operate together in a system to regulate extracellular potassium concentration in response to commonly encountered challenges. In addition, interactions between potassium regulation and commonly used medications will be considered in Chapter 6, and in Chapter 7 the causes and treatment of dysregulation of potassium will be discussed.