The Oskar Diethelm Library is a special collection devoted to the history of psychiatry. It is part of Weill Medical College’s Institute for the History of Psychiatry and includes approximately 50,000 titles in English, French, and German dealing with psychiatry, psychology, psychoanalysis, mesmerism, spiritualism, phrenology, witchcraft and related topics. Journal holdings include long back runs of psychiatric journals as well as current journals dealing with the history of medicine, psychiatry and psychology. Archival holdings include the papers of numerous organizations and individuals. The Library is open to qualified scholars in the history of psychiatry and related fields Monday through Friday, 10am to 5pm by appointment. Photocopying is available.

The Library counts among its holdings nearly every edition of the monographs of important figures such as Emil Kraepelin, Sigmund Freud, Isaac Ray and Benjamin Rush. Holdings include significant collections of works in such areas as the history of hypnotism and psychoanalysis, the American mental hygiene movement, and the temperance movement, as well as religious and medical debates on witchcraft, suicide, and sexual behaviors. There are also many early and rare first-person accounts of psychiatric illness, alcoholism, and drug abuse. A collection of hospital and asylum reports of the 19th and early 20th centuries has been amassed, amounting to more than 3,500 items. The Library holds approximately 1300 volumes that pre-date 1801 including nearly 500 early medical dissertations of psychiatric interest published before 1750.

Archival holdings include approximately 60 collections of papers from individuals and organizations vital to the history of psychiatry. Notable collections include the records of the American Psychoanalytic Association, the National Committee for Mental Hygiene, and the Group for the Advancement of Psychiatry. The Library holds the papers of D.W. Winnicott and David Levy, making it an important resource for the study of child psychiatry and psychoanalysis. Other individual collections of interest are the papers of psychiatrist Thomas W. Salmon, Clifford Beers, the founder of the American mental hygiene movement, and Jonathan Webster, a mesmerism practitioner.