From the NYPL web site:
"The Jerome Robbins Dance Division of The New York Public Library is the largest and most comprehensive archive in the world devoted to the documentation of dance. Chronicling the art of dance in all its manifestations - ballet, ethnic, modern, social, and folk - the division is much more than a library in the usual sense of the word. It is part museum, part film production center, and part consulting service to the professional dance community. It preserves the history of dance by gathering diverse written, visual, and aural resources, and it works to ensure the art form's continuity through an active documentation program."