Sei Shōnagon's "pillow book" is the sole surviving Heian-period work of what was probably a widespread practice among literate men and women of keeping a journal by their pillows in which to record stray thoughts and impressions. Such informal collections of notes constituted a genre of prose fiction in Heian times that continued to evolve into the Japanese literary form called zuihitsu, a kind of free-association, "following the brush."

‍   Structured in but the loosest fashion, The Pillow Book can be picked up and dipped into completely at random. The earliest extant versions of this work date to 500 years after Shōnagon wrote it, and there is no way of telling whether the order of entries is the same she originally put them in or not. Nevertheless, the insights, gossip, character sketches, poetic fancies, and likes and dislikes she jotted down seem as fresh today as they undoubtedly did a thousand years ago.

‍   The book is made up of discrete units, most of which begin by stating a category, and then go on to record some observation upon it. To choose, at random:

Things that appear to disadvantage when painted:

Dianthus, cherry blossoms, yellow roses. Men or women who are praised in romances as being beautiful.

Things that appear to advantage when painted:

Pines. Autumn fields. Mountain villages and paths. Cranes and deer. A very cold winter scene; an unspeakably hot summer scene.

Other items include anecdotes and stories concerning Empress Teishi, her brother Korechika, and the various men Shōnagon flirted with. The Pillow Book has been translated into English by Ivan Morris (1991) and Meredith McKinney (2007).