Following the foundational overview presented in Chap. 1 , this chapter offers an interdisciplinary synthesis of the conceptual and empirical underpinnings of well-being. It aims to trace the philosophical and historical origins of happiness and subjective well-being (SWB), while systematically examining its multidimensional nature through biological-evolutionary, psychological, and sociocultural lenses. The chapter begins by exploring ancient Eastern and Western philosophical traditions—including Aristotelian eudaimonia, Epicurean hedonism, Stoicism, Confucianism, Daoism, and Chinese Buddhism—to establish the diverse theoretical roots of contemporary well-being research. Section 2.2 investigates the biological and evolutionary bases of SWB, incorporating genetic, neurobiological, and physiological perspectives to elucidate the mechanisms underpinning positive affect and resilience. Section 2.3 reviews key psychological models and theoretical advances, from early affect-based paradigms to integrated frameworks such as Ryff’s psychological well-being model, Self-Determination Theory, and the PERMA model. Finally, Sect. 2.4 adopts a sociocultural perspective, analyzing how cultural dimensions, social structures, and globalization shape conceptions and experiences of happiness across contexts. By integrating multidisciplinary insights, this chapter provides a comprehensive theoretical foundation for understanding well-being as a complex, dynamic construct, setting the stage for the applied and extended discussions in subsequent chapters.