[Lonely. Social, Ecclesiastical and Diaconal Perspectives] Lonely is the one who feels lonely. Ten to twenty percent of Germans are affected by loneliness - made more acute by the Covid-19 pandemic. Unlike being alone, loneliness is accompanied by painful feelings, cannot be ended voluntarily and causes stress to well-being and health. How does loneliness arise? How is loneliness related to ones self-image, competence in relationships, and sense for meaning of life? What theological perspectives exist on loneliness? Where do people experience loneliness in church contexts or diaconal fields of action? What strategies and concepts can be used to counter loneliness? Should we also consider loneliness prevention, e.g., teaching mental health skills and strengthening interpersonal relationships at an early age? These and other questions are explored in this volume of essays.