Ottilie Ethel Leopoldine Herbert, Countess of Carnarvon (née Losch; 1903–1975), known professionally as Tilly Losch, was an Austrian dancer, choreographer, actress and painter. A graduate of the Vienna Opera Ballet School, Losch worked with Max Reinhardt for productions such as of A Midsummer Night's Dream (1927) and The Miracle (1932).

The Tilly Losch collection consists of incoming and outgoing correspondence as well as legal documents, banking records, personal memorabilia, diaries, engagement books, press clippings, photographic portraits, and publicity photos. The collection also includes a large number of loose sketches, sketchbooks, and personal memorabilia and more than 500 of her paintings, many dealing with autobiographical themes. The collection loosely spans the years 1910-1975. The major portion, however, represents materials she accumulated during the many years she lived and worked in America, roughly from the 1930s to the time of her death in 1975. The bulk of this material pertains to her post-dancing career, when she was active as a painter, model and socialite, although numerous photographic studies document her dancing and film career as well.

The largest portion of the collection comprises incoming and outgoing personal correspondence with family and friends, as well as business and legal correspondence. Correspondents include European and American artistic, literary, theatrical, and social personages, some well known in their day. The arrangement is alphabetical for incoming correspondence and topical for outgoing correspondence. Newspaper clippings regarding her career as dancer, actress, painter, model and socialite from the 1920s on are also arranged topically. A subsequent portion of the collection contains primarily photographic portraits and is arranged alphabetically by photographer and production. Finally, a large number of working sketches, sketchbooks and finished paintings as well as assorted memorabilia in no particular order or sequence comprise the collection. The paintings, being of varying sizes and shapes, are stored separately.

The Tilly Losch collection represents a valuable resource for both practitioners and historians of twentieth-century arts and culture. As an important figure in the world of classical and modern dance, her career illustrates many aspects of the large-scale intellectual and cultural migration from Europe to American from the 1920s to the 1940s. While her earlier dancing career is closely associated with Max Reinhardt's theatrical enterprises, she also adapted successfully to the new world of Broadway musicals and Hollywood films. Her biography and career reflect the successes and tribulations that European émigrés faced in America, as well as the process of cultural transmission and the enrichment they brought to American artistic life.