This chapter introduces the book’s purpose and scope, highlighting the complexity of loneliness and arguing that our understanding remains incomplete, despite extensive research. The book challenges the view of loneliness as merely an individual issue, emphasizing the role of community and societal influences. It focuses on older adults, specifically those aged 65 and over, distinguishing between the third age (typically between 65 and 80), marked by independence and good health, and the fourth age (80+), characterized by physical and mental decline and increased loneliness. After a brief sketch of the history of loneliness research, describing the first and second generations of loneliness, it explains the challenges in measuring loneliness and the complications of unraveling the often overlapping macro-level impacts on loneliness. By systematically developing and integrating macro-level perspectives with existing understandings of loneliness, this book advances the field by exploring the social construction of loneliness and the impact of macro-level factors such as digitalization, climate change, and societal crises. These influences shape both individual experiences and broader societal conditions affecting social connection. The chapter concludes by explaining the structure of the book and future research directions, aiming to expand both theoretical understanding and practical strategies for addressing loneliness at the individual, community, and societal levels.