The lungs and kidneys are cooperative and interdependent organs that secure the homeostasis of the body. Volume and acid–base disorders sit at the nexus between these two systems. However, lung–kidney interactions affect the management of many other conditions, especially among critically ill patients. Therefore, management of one system cannot proceed without a thorough understanding of the physiology of the other. This installment of AJKD’s Core Curriculum in Nephrology discusses the complex decision-making required in treating concomitant respiratory and kidney disorders.