Extending the Book introduces the largely-forgotten art of extra-illustration - individually adding portraits or other illustrations to published books - and explores what this personalized form of book design reveals about the history of reading.

It includes a brief introduction to the concept of designing and creating a unique book by adding external material and an overview of the phenomenon's history and its heyday in the later eighteenth and nineteenth centuries. The works of Shakespeare - the most popular single author for extra-illustration - exemplify the practice as it changed over time.

From the beginning, extra-illustrators had to defend the "exquisite handicraft" (in the words of an 1890 proponent) against accusations of "breaking up a good book to illustrate a worse one" (in the words of an 1892 critic). This book examines the art and the practice of extra-illustration, from crudely altered books to beautiful new creations.