Immune aging is the progressive, age-associated decline and functional dysregulation of the immune system, a process also referred to as immunosenescence. As a research concept, it encompasses the comprehensive study of the complex cellular, molecular, and physiological alterations that occur within both innate and adaptive immunity over time, compromising effective immune responses. This field investigates changes such as thymic involution, alterations in lymphocyte populations and function, dysregulated cytokine production, and the development of chronic low-grade inflammation (inflammaging). Its significance lies in its critical role in increasing susceptibility to infections, reducing vaccine efficacy, contributing to the pathogenesis of chronic age-related diseases, and impacting overall health span and longevity in older populations.