This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book examines the relationship between social class and mental disorders in Northern Europe between the late 19th and late 20th centuries. During this period the number of patients confined in mental hospitals increased to the point where they were often overcrowded and understaffed by the outbreak of World War II. In the 1950s and the 1960s, mental health studies on the American population confirmed this thesis that the prevalence of mental illness is to some extent dependent on the socioeconomic status of individuals. The book focuses on the close link between the socioeconomic status of mental patients and the health care provided for them in public institutions. It examines the various ways in which social class made itself visible, not only on the wards of mental hospitals, but also in the establishment of the very institutions themselves.