Milk ejection, also known as the “milk let-down” reflex, represents one of the most important examples of neuroendocrine integration in mammalian physiology. It is a rapid, highly coordinated process through which milk, which is stored in the alveoli of the mammary gland, is expelled into the larger ducts and cisterns in response to the suckling stimulus. This phenomenon primarily depends on the secretion of oxytocin from the posterior pituitary gland, which then acts on myoepithelial cells surrounding the alveoli and results in contraction of alveoli and milk expulsion. Although the reflex has been extensively studied in dairy science due to its direct relation to milk yield, its physiological, evolutionary, and neurobiological implications extend far beyond dairy importance. The milk ejection reflex (MER) provides a window into neuroendocrine control of behavior, maternal bonding, and the plasticity of the hypothalamo–hypophyseal system. Understanding the comparative aspects of this reflex across species offers insights into adaptive lactation strategies, the evolution of maternal behavior, and the regulation of oxytocin release in health and disease.