Metadata, by definition, is data about data. In the case of books, metadata can include information such as the title, author, publisher, publication date, ISBN, and genre. This metadata is crucial for organizing, cataloging, and discovering books, both in physical and digital formats. The use of metadata has evolved over time but it has existed nearly as long as books themselves.

The term 'metadata' was first coined by Philip Bagley in his book "Extension of Programming Language Concepts," in a context not at all related to books or other physical objects, but the term turned out to be a useful one to describe sets of data in a wide variety of applications.

Book metadata has existed long before before the term was coined. One of the earliest examples of book metadata can be found in the Great Library of Alexandria, dating back to around 280 BC. Librarians at the time attached small tags to the end of scrolls, which included details such as the title, subject, and author of the work.

In medieval times, scholars used several different ways to record metadata about manuscripts, including written inventories of their manuscripts, shelfmarks, which marked a manuscript's particular place on a shelf, colophons, or inscriptions, usually at the end of a manuscript, providing information about the scribe's name, date of completion, place of production and other information useful for cataloging and provenance.

Some larger institutions, like the University of Paris, developed more sophisticated library catalogs. These catalogs could include detailed descriptions of the manuscripts, including their physical characteristics and contents. These medieval cataloging methods were the precursor to the card catalogs found in libraries for hundreds of years.

The first library card catalog was created in 1791 by the Revolutionary Government in France. They used playing cards, which were blank on one side and readily available. This innovation marked a significant step in the evolution of library cataloging, making it easier to organize and access books. Card cataloging became commonplace in libraries,but it took many years before the card catalog system was standardized.

In 1908, the American Library Association (ALA) established standards for card catalog formats in American libraries. The ALA set guidelines for the size of library catalog cards, which enabled the uniform production of both cards and storage cabinets. This standardization streamlined the cataloging process and facilitated information sharing among libraries.

Europeans, seeing the success of standardization in America, were quick to follow suit in the late 19th and early 20th centuries. The International Federation of Library Associations and Institutions (IFLA) significantly promoted standardization across Europe. They worked on developing international cataloging standards, which included card formats.

In 1971, the Library of Congress in the U.S. initiated a Cataloging in Publication (CIP) program. The CIP data, supplied by the Library of Congress and printed on the copyright page of each book by the publisher, provides essential bibliographic information that helps libraries and book dealers catalog and process books more uniformly, efficiently and accurately.

In the mid-20th century, libraries moved from physical card catalogs to digital databases, enabling more advanced search and organization capabilities. Today's online catalogs offer greater flexibility and space than the small card catalogs of the past. They include standard metadata like title, author, subject, and page count, in addition to expanded information on copyrights, licensing, sales, marketing, and enhancements such as cover images, synopses, reviews, and author biographies.

Today, book metadata is essential for e-commerce, digital libraries, and online discovery. Publishers, libraries, and third-party organizations collaborate to create and maintain comprehensive metadata standards to ensure books can be easily identified, located, and purchased in the digital age.

It is possible that the future includes the obsolescence of book metadata, as large language models (LLMs) index the full-text of more of the world's published books. Scholars and Librarians need not reference metadata if a search can find data from any page or paragraph of any book with a simple query.