I didn’t always care about book indexes. For years, I treated them the way most readers do: as that dense block of tiny text at the back, something to flip past on the way to confirming I’d actually finished the book. Then I started working in publishing, and my opinion changed fast. A good index is one of the most useful tools a reader can have, and a bad one (or worse, a missing one) can turn an otherwise solid book into a frustrating experience.

Let me be clear about what I mean. I’m not talking about fiction. Nobody needs an alphabetical listing of every character appearance in a novel. I’m talking about nonfiction: history, science, biography, reference works, how-to guides, academic texts. These are the books where you’re likely to return to a specific passage, look up a specific claim, or try to find that one paragraph you half-remember from three chapters ago. Without a proper index, you’re stuck thumbing through pages or, if you’re reading digitally, relying on a search function that returns every instance of a common word with zero context.

The difference between a search function and a good index is the difference between a phone book and a knowledgeable friend. A search function tells you where a word appears. An index tells you where an idea lives. That distinction matters more than people realize.

What an Index Actually Does

At its most basic, an index is an alphabetically organized guide to the contents of a book, listed by subject, name, and concept with corresponding page numbers. But that description makes it sound mechanical, like something a computer could spit out in seconds. In reality, professional indexing is interpretive work. The indexer has to read the entire book, understand its arguments, and then decide how a future reader might try to find information within it.

Think about that for a moment. The indexer isn’t just listing words. They’re anticipating questions. If I write a book about the history of bread, and I mention sourdough starters on page 47 in the context of Gold Rush-era San Francisco, the indexer needs to decide: does this entry go under “sourdough,” under “San Francisco,” under “Gold Rush,” or under all three? And should there be a cross-reference from “starters, sourdough” to “sourdough starters”? What about “fermentation”? The bread itself might be the topic of the sentence, but the underlying point might be about westward migration and food culture.

A good indexer captures all of those threads. A mediocre one just lists the obvious nouns. And an automated one, generated by software that scans for proper nouns and high-frequency terms, misses the nuance entirely.

The History of Indexing Is Stranger Than You’d Expect

People have been making indexes for a surprisingly long time, though not always in the form we recognize today. The concept of organizing information alphabetically took centuries to become standard. In the ancient world, scrolls didn’t lend themselves to random access the way codices (bound books) did. You couldn’t easily flip to page 200 of a scroll. So early reference systems relied on memory, marginal notes, and tables of contents rather than back-of-book indexes.

The shift to the codex format in the early centuries of the Common Era made indexing possible, but it took a while for anyone to bother. Monastic scholars in the medieval period started compiling concordances, particularly for the Bible, which were essentially exhaustive indexes of every word and where it appeared. These were enormous projects, sometimes filling multiple volumes on their own. The idea was that a preacher preparing a sermon on, say, mercy could quickly find every biblical passage that mentioned mercy without reading the entire text from Genesis to Revelation.

By the 13th century, scholars at the University of Paris had produced some of the first true concordances of the Bible. These were collaborative efforts involving dozens of monks, and they required a standardized system of chapter and verse divisions, which hadn’t existed before. So in a real sense, the desire for better indexes helped create the chapter-and-verse system we still use today. The index didn’t just organize information. It reshaped how we structured books.

The printing press accelerated everything. Once you could produce hundreds of identical copies of a book, page numbers became consistent across copies, and a proper index became feasible. Before printing, every manuscript was unique, with different page layouts, and an index keyed to one copy would be useless for another. After Gutenberg, an index in one copy worked for every copy. That’s when the back-of-book index as we know it became standard practice for scholarly and reference works.

Why Publishers Sometimes Skip the Index

Given how useful indexes are, you might wonder why some nonfiction books don’t have them. The answer is almost always money and time. Professional indexing costs between $3 and $8 per page, sometimes more for technical or specialized content. For a 400-page book, that’s $1,200 to $3,200, and it has to happen at the very end of the production process, after the final page proofs are set, because page numbers can shift during typesetting. That means the indexer is working under a tight deadline, often just a couple of weeks, right when everyone involved in the book is exhausted and eager to be done.

Some publishers push the cost onto the author. I’ve seen contracts that specify the author is responsible for providing or paying for the index. For a first-time author who just spent two years writing a book and might be earning an advance of $10,000 or less, an extra $2,000 for indexing feels like a lot. Some authors try to do it themselves to save money, and the results are usually disappointing. Indexing your own book is like editing your own book: you’re too close to the material to see it the way a reader would.

At ScrollWorks, we consider the index part of our production budget, not the author’s problem. I feel strongly about this. If we’re publishing a nonfiction book, we’re committing to making it useful, and that means including a professional index. It’s not optional. It’s not a luxury. It’s a basic component of a finished nonfiction book, like a table of contents or page numbers.

The Qualities of a Great Index

Not all indexes are created equal, and once you start paying attention, you’ll notice the difference between a thoughtful one and a lazy one. Here’s what separates the good from the great.

First, a great index uses language the reader would actually use. If the book discusses “quantitative easing” but a general reader might look for “money printing” or “Federal Reserve policy,” the index should include cross-references from those terms. The indexer has to think like the reader, not like the author. This is why automated indexes fail so badly: they only capture the author’s vocabulary, not the reader’s.

Second, a great index breaks down broad topics into useful sub-entries. An entry that says “World War II, 23, 45, 67, 89, 102, 115, 134, 156, 178, 201, 223” is worse than useless. It tells you the topic appears frequently but gives you no way to find the specific aspect you’re interested in. A better entry would be “World War II: causes of, 23-28; Pacific theater, 67-89; home front economics, 102-115; Allied strategy in Europe, 134-156.” Now you can actually find what you need.

Third, the index should include concepts, not just proper nouns. A biography of Thomas Edison should index “filament experiments” and “patent disputes” and “laboratory culture,” not just the names of people and places. The conceptual entries are often the most valuable ones, because they help you find the analytical meat of the book rather than just the narrative surface.

Fourth, and this is subtle, a great index reflects the book’s argument. If a history book is making the case that economic factors drove a particular political change, the index should make it easy to trace that argument across chapters. The index becomes a kind of map of the book’s intellectual structure, and a skilled reader can sometimes evaluate a book’s argument just by studying its index.

The People Who Make Indexes

Professional indexers are a fascinating group. Most of them are freelancers. Many have advanced degrees in the subjects they index. They tend to be voracious readers with a particular talent for categorization and an almost obsessive attention to detail. The American Society for Indexing (ASI) has been their professional organization since 1968, and they hold annual conferences where people discuss things like the proper handling of “see also” references and whether to use letter-by-letter or word-by-word alphabetization. I went to one of these conferences a few years ago and found it genuinely interesting, which probably says something about me.

The pay isn’t great for the amount of skill involved. Most indexers charge by the page or by the entry, and even experienced ones typically earn between $25 and $40 per hour when you account for all the reading and analysis time. It’s the kind of work that attracts people who love books and language and don’t mind working alone. I’ve met indexers who specialize in medical texts, legal texts, cookbooks, children’s encyclopedias, and everything in between. Each specialization requires different knowledge and different conventions.

There’s a persistent myth that indexing will be fully automated soon, and it keeps getting repeated by people who’ve never actually compared an automated index to a human one. Yes, software can generate a concordance. It can identify every instance of a proper noun and list its page numbers. What it can’t do, at least not yet, is understand that a paragraph about “the president’s economic advisor” on page 156 should be indexed under the advisor’s name even though the name doesn’t appear on that page, because the advisor was introduced by name on page 154 and referred to by title for the next three pages. A human indexer catches that. Software doesn’t.

Digital Books and the Index Problem

E-books have complicated the index question in ways that publishers are still figuring out. On one hand, digital books have built-in search functions, which makes some people argue that indexes are unnecessary in digital formats. On the other hand, as I mentioned earlier, searching and indexing are fundamentally different activities. A search for “Jefferson” in a digital book about American history will return dozens or hundreds of hits with no indication of which ones are substantive discussions and which are passing mentions. An index entry for “Jefferson, Thomas” with sub-entries telling you where to find his views on agriculture versus his diplomatic career versus his relationship with Sally Hemings is infinitely more useful.

The technical challenge with e-book indexes is that page numbers aren’t fixed. Depending on your device, your font size settings, and your display preferences, the “pages” in an e-book are fluid. So a traditional index keyed to page numbers doesn’t translate directly. The solution most publishers have adopted is to hyperlink index entries directly to the relevant passages, which actually works better than page numbers in many ways, because you can tap an entry and jump straight to the text. But creating a hyperlinked index is more work than creating a traditional one, because every entry needs to be linked to a specific anchor point in the text, not just a page number.

Some publishers have decided it’s not worth the effort and simply omit the index from the e-book edition. I think this is a mistake. If anything, e-book readers need indexes more than print readers, because they can’t easily flip through physical pages to find something they vaguely remember. The search function is a poor substitute, and without an index, readers are left with a worse experience than they’d have with the print edition.

Famous Indexes and Infamous Ones

There’s a small but entertaining tradition of authors using the index to settle scores or make jokes. The poet Alexander Pope reportedly included mocking index entries in his satirical work “The Dunciad,” pointing readers to passages that ridiculed his literary enemies. More recently, some authors have used index entries as a form of dry commentary. I once encountered an index entry that read “meetings, pointless: see also bureaucracy” in a book about organizational management, which told me everything I needed to know about the author’s perspective.

On the other end of the spectrum, there are infamously bad indexes. The most common failure mode is the “concordance masquerading as an index,” where every significant noun gets listed with a string of undifferentiated page numbers and no sub-entries. This is technically an index in the same way that a phone book is technically a social network: it contains the right information but in a form that’s nearly impossible to use efficiently.

Another common failure is the vanity index, where the author indexes themselves on practically every page. “Smith, John: 1-350” is not helpful. It’s just the author confirming that they wrote the book, which the reader presumably already knew.

What Readers Can Learn from Indexes

Here’s something I recommend to anyone who reads a lot of nonfiction: before you start a book, read the index. Not word by word, but scan it. Look at what topics get the most space. Look at which names appear most frequently. Look at the sub-entries under major topics. You’ll get a surprisingly accurate sense of the book’s priorities and approach before you read a single chapter.

I also use indexes to evaluate books I’m considering acquiring for our list. If I’m looking at a manuscript about, say, the history of jazz, and the index (or proposed index structure) doesn’t include entries for specific recordings, specific venues, or specific musical techniques, that tells me the book might be too general, too focused on biography at the expense of the music itself. The index reveals what the book actually covers versus what the title promises.

Academics have known this trick for decades. When a scholar is researching a topic and evaluating whether a particular book is worth reading in full, they often start with the index. If their specific area of interest appears in the index with substantial sub-entries, the book is worth their time. If it appears only in passing or not at all, they can move on. The index functions as a contract between the book and the reader: these are the subjects I address, and here’s where to find them.

The Future of Indexing

I think about the future of indexing more than most people, probably because I see the consequences of both good and bad indexes on a regular basis. AI tools are getting better at natural language processing, and there are products on the market that claim to generate usable indexes automatically. I’ve tested several of them, and my honest assessment is that they’re useful as a starting point but nowhere near ready to replace human judgment. They can identify the obvious entries, the proper nouns, the chapter headings rephrased as index terms. But they miss the subtle connections, the implied references, the conceptual threads that make a great index great.

My prediction is that we’ll see a hybrid approach become standard over the next decade. Software will generate a draft index, and a human indexer will refine it, adding the conceptual entries, fixing the cross-references, and ensuring the sub-entries actually help the reader rather than just listing page numbers. This could bring down costs and speed up the process, which would be good for everyone. But it won’t eliminate the need for human indexers, because the core skill, understanding what a reader might look for and how they might look for it, is fundamentally a human one.

In the meantime, I’d encourage you to pay attention to the indexes in the books you read. Notice when they’re helpful and when they’re not. Notice when a book doesn’t have one and how that affects your ability to use it as a reference. And if you’re an author working on a nonfiction book, please, for the love of your readers, budget for a professional index. Your book deserves it, and so do the people who read it.

At ScrollWorks Media, every nonfiction title we publish, from Bitcoin for Absolute Beginners to our forthcoming releases, gets a professionally crafted index. We think of it as part of the reader’s experience, not an afterthought. If you’re curious about our catalog and how we approach book production, take a look at our full list of titles.