André Hajek is Professor for Interdisciplinary Health Care Epidemiology, Department of Health Economics and Health Services Research at the University Medical Center Hamburg-Eppendorf, Germany.

Steffi G. Riedel-Heller is Professor of Social Medicine and Public Health, and Director of the Institute of Social Medicine, Occupational Health and Public Health (ISAP), University of Leipzig, Germany.

Hans-Helmut König is Professor of Health Services Research and Health Economics, and Director of the Department of Health Economics and Health Services Research at the University Medical Center Hamburg-Eppendorf, Germany.

0.Preface. Part One - Concepts: Loneliness and social isolation. [...] concepts and measurement of social isolation and loneliness. Part Two - Correlates of loneliness and social isolation in old age: Overview. 2. Impacts of loneliness and social isolation on healthy longevity in older adults. Part Three - Correlates of loneliness and social isolation in old age: Socioeconomic factors. 3.Socioeconomic correlates of loneliness and social isolation in late life. 4.Correlates of loneliness and social isolation in old age: Poverty. 5.Culture, social isolation and loneliness in later life. Part Four - Correlates of loneliness and social isolation in old age: Lifestyle-related factors. 6.Loneliness and Social Isolation Among Older Informal Caregivers: A Review of the Evidence From Longitudinal Investigations. 7.Grandchild care and loneliness. [...] ownership, Loneliness and Social Isolation. 9.Online social media use, loneliness and perceived social isolation in later life: A short overview and some empirical evidence. 10.Lifestyle-related factors in loneliness and social isolation of older persons: A Ghanaian study. Part Five - Correlates of loneliness and social isolation in old age: Health-related factors. 11.Health comparisons and loneliness and perceived social isolation: A brief overview and empirical evidence. 12.Obesity and loneliness in old age: Associations with weight stigma. 13.Frailty and loneliness/social isolation in late life. 14.Multimorbidity, Loneliness, and Social Isolation. A Systematic Review. 15.Social Isolation, Loneliness and Mental Health in Old Age. Part Six - Policy implications and future of loneliness and social isolation. 16.Public Policy and the Reduction and Prevention of Loneliness and Social Isolation. 17.Loneliness during the COVID-19 pandemic. Part Seven - Overview: Longitudinal aging studies around the world available to researchers. 18.Overview: Loneliness and social isolation in longitudinal aging studies around the world.