Homeostasis, a key concept in biology, refers to the tendency toward stability in the various bodily states that make up the internal environment. Examples include temperature regulation and oxygen consumption. The body's needs, however, do not remain constant. When an organism is under stress, the central nervous system works with the endocrine system to use resources to maintain the overall viability of the organism. The process accelerates the various systems' defenses of bodily viability, but can violate short-term homeostasis. This allostatic regulation highlights our ability to anticipate, adapt to, and cope with impending future events. In Rethinking Homeostasis, Jay Schulkin defines and explores many aspects of allostasis, including the wear and tear on tissues and accelerated pathophysiology caused by allostatic overload. Focusing on the concept of motivation and its relationship to central nervous system function and specific hormonal systems, he applies a neuroendocrine perspective to central motive states such as cravings for water, sodium, food, sex, and drugs. He examines in detail the bodily consequences of the behavioral and neuroendocrine regulation of fear and adversity, the endocrine regulation of normal and preterm birth, and the effects of drug addiction on the body. Schulkin's presentation of allostasis lays the foundation for further study.