The book has for centuries been a reassuringly definite artefact, although many aspects of its existence and circulation are quite intangible and its ultimate effects seem universal if not limitless. Paradoxically, the physical variations in different copies of a book seem to demand that we understand the book not as precisely defined artifact but as elusive, conceptual "work" or "text". Sometimes too, the value and meaning of the book are seen to reside not in its core content but rather in the aesthetics of its design or book-making. Although the sequentially-read codex has been the normative form of the book for many centuries, alternative physical forms ranging from the scroll to a box of randomly ordered sheets, to a dossier of facsimile documents, to an electronic tablet challenge and extend the category of object we call "book."

Books exist also through their effects on readers, and are limited or liberated by the networks of commercial and personal circulation that develop and change over time. Extreme forms of this tension between object and effect are books that circulate by repute without ever having actually existed, books that seek to escape limitation or appropriate additional cultural capital by misinforming the readership about their contents, genesis or provenance, or books that are known to have circulated, but have since disappeared.

No technological innovation has more sharply raised the issue of the potential and the limits of the book than the development of digital textuality. While the eschatological promises of the late 1980s and early 1990s may seem risible in retrospect, writing and reading digital texts have become thoroughly normalized practices for much of the western world, so that few books today are untouched by digital processes. It remains to be seen whether this digitization will be the destroyer of the book or the infinite extender of its limits.