What Is Book Indexing? The Navigation Tool That Makes Nonfiction Books More Usable

If you’re an author who’s poured months—or years—into writing a nonfiction book, you’ve probably focused on the content itself. What often comes as a surprise is that, once the writing is done, and you're off to the copyediting stage, there’s one manuscript element that can dramatically affect how readers actually use your book: the index!

A book index isn’t an optional extra or a technical afterthought—it’s a reader-facing navigation tool that helps people quickly find the ideas they need. For many nonfiction books, an index improves usability, credibility, and even sales, yet many authors don’t encounter indexing until late in the publishing process. To clarify what indexing really is and whether your book needs one, I interviewed my colleague and indexing expert Heather Pendley of Pendley’s Pro Editing & Indexing.

*Note: Memoirs, personal narratives, low-content books (journals, planners), children's picture books/early readers usually do not need to have an index.

This interview has been edited for length.

What Professional Indexing Covers

Linda: Can you explain, in simple terms, what a book indexer does and why indexing is important for nonfiction books?

Heather: An indexer’s goal is to make a book more accessible, whether its audience will read it from cover to cover or consider only certain chapters. We identify what a reader is likely to look up and create an index based on the manuscript. We organize concepts hierarchically and create cross-references (like see and see also) because many concepts are interrelated. A good index can dramatically improve a book’s usefulness, credibility, and salability; bookstores and libraries usually review a book’s table of contents (TOC) and index to make buying decisions.

L: What makes a professionally created index different from an automatically generated index or a simple keyword list?

H: A keyword list (or search feature) doesn’t include essential ideas or clarify the relationship between topics. A book on water might include many cross-references; something search can’t do:

It also often presents dozens of unorganized hits when searching for a certain term—if the inquiry was spelled correctly and exactly—causing a frustrated reader to give up after flipping back and forth several times still not finding what they want. Notice how the exact same page numbers are listed below; one is the result of a digital search of the term U.S. Fish and Wildlife Service, the other is a properly analyzed index entry. Which is more useful?

In one book, the search feature revealed 28 hits for U.S. Fish and Wildlife Services, but it was a long string of page numbers with no description (“undifferentiated locators”). An index would organize the same pages in up to 13 subheadings, saving the reader time and headache.

L: Is indexing something that someone could do with AI?

H: AI-generated indexes are guilty of severe under-indexing when not hallucinating, preventing readers from finding what they seek and breaking their trust. The “structure” generated is insufficient or nonexistent, especially cross-references that link related topics.

With AI, entries are autocompleted based on statistical likelihood, often omit key ideas, can’t fine-tune terminology for easy retrieval, nor build the needed hierarchies of ideas that a professional indexer can. AI cannot understand context as the human brain does. And indexes are all about context.

The American Society for Indexing (ASI) released a white paper (https://asindexing.org/ai-news/white-paper-ai-index/) that goes into more detail of AI’s shortcomings. Writers should consider all the time, effort, and brainpower that went into their book and want to ensure their index is created by a human indexer who can personalize, edit, and fine-tune it.

L: My prescriptive nonfiction clients have been lucky to work with you on their books, but for those that have never used an indexer before, at what point in the publishing process should a writer hire an indexer and why does timing matter?

H: An indexer should be engaged early enough to allow time to create a thorough and useful index—usually when a book is finished and headed toward editing. A BOB (back-of-the-book) index is best created by referencing paginated proofs, most likely a PDF [indexers work on finished files, meaning manuscripts that have already been copyedited and laid out by a graphic designer]. For an embedded (hyperlinked) index, I require an InDesign or Word file.

In my experience, too often, writers or publishers don’t realize that indexers can have full schedules weeks or months in advance. And others seem not to know they even need an index until it suddenly becomes a rush job. Since an index can add great value to a book, it should not be an afterthought.

L: Are there things an author should not change once indexing begins? For example, layout, pagination, or chapter titles?

H: Nothing should be changed once indexing begins; it is the penultimate step before publishing (a final proofread is last).

Proofreading of the whole text might occur at the same time as indexing but are best done by different professionals as they require completely different mindsets.

In an emergency, most indexing software can repaginate an index easily enough, however, if moved chapters/sections aren’t full pages, it can be a big issue. Again, there is a bit more leeway with an embedded index than a BOB index, but there is always a risk that something will be lost if text is moved around.

L: What information or context is most helpful for an indexer to know about the book (audience, key terms, comparable titles)?

H: Audience is most important. Does the prospective reader have specialized subject knowledge or is the book on a topic completely new to them? If I know the target audience is the average lay person, not a medical professional, I must anticipate terms they’d probably look up, even if the exact words aren’t used in the text. (Another area where the search function fails.)

L: I'm a big advocate of empowering writers with knowledge so they can use their time and budget wisely. What should writers look for when choosing an indexer—training, experience, genre specialization, sample indexes?

H: Training is vital. I’ve seen poorly written and low-quality indexes that ultimately detracted from the books the index was meant to enhance. Consulting the ASI Indexer Locator list (or another well-known indexing organization) helps ensure clients work with trained professionals. The Locator List allows authors and publishers to search by subject specialty (such as history, music), type of material (for example cookbooks, instruction manuals), language expertise and software proficiency. [It's ok to ask for a sample of previously created indexes as a form of reference].

Good indexing is intellectual and judgment-based; a popular refrain of indexers when considering whether certain entries should be included in an index is “it depends.”

An index should sufficiently reflect the text and be appropriate for the audience; a comprehensive index is likely required for a scholarly text while a guide book would be less detailed. Length restrictions may also affect the index, but term choice must always be succinct and clear. [To get an idea of how much you may have to spend to have your manuscript professionally indexed, calculate that here Editorial Freelancers Association Rate Calculator.]

L: What are some common misconceptions authors have about indexing, and what do you wish more writers or publishers understood about the process?

H: Many believe an index is just an alphabetical list of important words with page numbers listing where they’re found, but that is a concordance. Some think an index is an elaborate table of contents, a book outline, or that a search feature is sufficient. Others think an author can write one quickly because they know the contents by heart, but writers are often tired of the subject, less objective, and most important, unfamiliar with what makes a good index.

What I wish more writers and publishers would realize was stated best by Nancy Mulvaney, author of Indexing Books:

"Indexing cannot be reduced to a set of steps that can be followed! It is not a mechanical process . . . it is a form of writing.”

L: Thank you Heather! If someone would like to talk to you about indexing their next book, where can they find you?

H: I'm best found by email at Heather@PendleysProEditing.com or PendleysProEditing.com. I'm also on LinkedIn, Instagram, and Facebook.

Heather Pendley is a freelance indexer, copyeditor, and owner of Pendley’s Pro Editing & Indexing (basically, she’s a big word nerd). Heather is American Society for Indexing’s training course administrator, has presented on indexing several times to various groups and conferences, served on EFA and SD/PEN boards, and judged an ACES Headline Competition. She loves indexing because it scratches the organizational itch in her brain, and she takes pride in helping authors present their best work. Heather lives in Southern California with her husband and two rescue dogs and spends significant time at various bookstores and libraries around the county.

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