The problem of loneliness has increased dramatically over the last 25 years. Loneliness presents a threat to the mental, emotional, and even physical well-being of the lonely individual. This statement is borne out in much research, and the alarming threat that loneliness presents is such that the U.S. Surgeon General issued an 82-page advisory in 2023 on what he called an ?epidemic? of loneliness. Here in this Handbook of Loneliness, are gathered experts on loneliness from all over the world, in multiple disciplines, in which they discuss the results of their research and that of their colleagues on a wide range of topics related to understanding loneliness. The Springer Handbook of Loneliness is an invaluable reference for anyone seeking a wide-ranging, deeper understanding of the causes and effects of loneliness, and how loneliness can be reduced.