Health is one of the most fundamental aspects of human life, as it plays a crucial role in shaping an individual’s overall well-being, happiness, and ability to function effectively in society. An optimal state of health influences both physical and mental well-being, enabling individuals to engage in daily activities with energy, focus, and resilience. Good health contributes to higher productivity, as it allows people to perform at their best in their personal and professional lives, reducing absenteeism and increasing efficiency. Importantly, maintaining optimal health can lead to increased longevity, ensuring a higher quality of life in later years. Health is not just a personal asset but also a societal necessity, as a healthier population leads to stronger economies, reduced healthcare burdens, and improved social stability. The health of individuals within a society contributes significantly to its overall social and economic well-being. Understanding health goes beyond merely the absence of disease or physical ailments; it encompasses a holistic state of well-being that includes physical, mental, and social aspects. This chapter provides an in-depth exploration of key concepts related to health, illness, well-being, and health behavior, highlighting their interconnected nature and the various factors that influence them. It examines how individuals experience and perceive health and illness, the psychological and social dimensions of well-being, and the ways in which personal and societal health behaviors contribute to overall health outcomes. Additionally, the chapter delves into the crucial role of environmental factors, both physical and social, in shaping health-related behaviors, access to healthcare, and overall quality of life. This chapter also introduces the core purpose of this handbook, outlining the scope of its contents and the key themes it covers. Readers will develop an understanding of key theoretical frameworks related to health, explore the factors influencing health behavior, and examine the crucial role of environmental determinants in shaping people’s health and overall well-being. By engaging with the material presented in this handbook, readers will develop a comprehensive understanding of health-related concepts and acquire practical knowledge that can be applied in various professional and personal contexts.