This article is a review of the current literature on loneliness. The relationship of loneliness to other variables, the major characteristics of the experience of loneliness, and a definition of loneliness for counseling are described. The unidimensional and multidimensional perspectives of the loneliness experience are illustrated, with special focus on how they relate to loneliness measurement. The incidence of loneliness among various populations is also discussed. Finally, treatment strategies for loneliness, which highlight cognitivebehavioral therapy, social skills training, and social support are provided, followed by suggestions and implications for counseling practice and research.