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This site is a database of images of variant handwritten hiragana and kanji, taken from documents as well as bamboo strips (mokkan 木簡) from the premodern period. Search by kana or kanji, and view images of variant ways of writing them.
Database of kuzushiji provided by the Historiography Institute of the University of Tokyo.
Texts with Honkoku
These digital archives contain page images of documents written in kuzushiji with hentaigana and kanji, and many also include honkoku 翻刻 that can be viewed alongside or superimposed on the original documents.
A variety of early modern books on Ise monogatari, accompanied by honkoku in a popup window. Note that you need to scroll through the honkoku as you turn pages, rather than receiving a new honkoku for each page.
This site provides high-quality scans of a copy of Genji Monogatari held by the Library of Congress, along with a transcription in tyeset Japanese either superimposed on the image or displayed alongside it.
The Hentaigana App or 変体仮名あぷり is a smartphone app that helps users learn to read hentaigana, by teaching which kanji each kana comes from and how to read it. Available in English and Japanese, for Android and iOS.
A database of seals stamped in books by collectors. The advanced search function is extremely detailed and allows you to search by size, color, title, author, etc. It provides high-quality digital images of the seals and notes which institution holds the book that was scanned.
These are sites with information about premodern books, or kotenseki 古典籍.
The Kotenseki Workshop sponsored by C. V. Starr East Asian Library and the Center for Japanese Studies, University of California, Berkeley, and the National Institute of Japanese Literature was held at the C. V. Starr East Asian Library on March 11, 2016. This guide contains PDFs of the presentation slides from that workshop.
A MOOC taught by Sasaki Takahiro and Ichinohe Wataru from Keio University on traditional Japanese books and book culture. This is an introductory course and is open to anyone with an interest in the history of Japanese books. A basic knowledge of the history of Japan and Japanese literature will be helpful but is not required. The course makes use of a number of visual resources; course videos are in Japanese with English subtitles.