Loneliness is a multifaceted and complex phenomenon that profoundly impacts individuals across the lifespan. It goes beyond mere social isolation, encompassing subjective feelings of emptiness and disconnection. Loneliness is influenced by a combination of biological, psychological, social, and environmental factors, and it can have significant implications for mental and physical health. This all-encompassing textbook thoroughly examines the various facets of loneliness, offering readers an in-depth exploration of its dimensions, prevalence, repercussions, and potential interventions. Crafted by esteemed authorities in psychology, neuroscience, sociology, and public health, the book presents a diverse perspective on loneliness, weaving together the most recent research discoveries with pragmatic insights. A significant portion of the book is dedicated to examining the role of social policies, community-based initiatives, and technology in preventing and alleviating loneliness.