Books in the Reizei family library include writings in Toshinari's and Teika's own hands, and even Teika's own personal diary, the "Meigetsuki" (Chronicle of the Clear Moon), making the library a treasure trove of important documents in the study of Japanese literature and medieval Japanese history.
冷泉家所蔵本は、俊成・定家の自筆本や、定家の自筆日記『明月記』をはじめ、日本文学や日本中世史の研究上、貴重な資料の宝庫である。