Longstanding evidence finds that healthy older adults tend to experience greater positivity, equanimity, and well-being in daily life. Prominent psychological theories of emotional aging tend to focus on cognitive pathways such as shifting motivations and accumulated cognitive resources (e.g., attentional control, expertise) to explain observed emotional aging effects. In this chapter, we introduce the physiological hypothesis of emotional aging (PHEA). At its core, the PHEA proposes that physiological aging contributes to emotional aging, wherein age-related changes to the peripheral body and how the brain represents and regulates the peripheral body (e.g., interoception) should result in age-related changes to emotional experience and associated socioemotional perceptions and behaviors, i.e., emotion communication. Importantly, the PHEA argues that the dynamics of physiological aging (e.g., increased dysfunction, greater afferent noise from the viscera and peripheral transmission pathways, reduced interoception) may in turn facilitate the increased importance of cognitive pathways in late life emotional outcomes and functions. As such, the PHEA provides an integrative neuroscience approach to emotional aging that highlights the importance of physiological health and aging across the body and brain while providing an interpretive framework that complements existing cognitive theories of late life emotion. This chapter introduces core arguments of the PHEA, unifies existing evidence on physiological, interoceptive, and related neural aging as relevant for emotional aging, and forecasts new directions and implications for late life socioemotional functioning and interpersonal behaviors.