Indexes and cross-references in an ebook
Your paperback ends with eleven pages of index. The ebook is the same manuscript, so the index goes in as well, and the ebook now ends with eleven pages of numbers that point at nothing.
A reflowable file has no fixed pages to point at: the page is assembled on the reader's device, out of their screen and their type size, at the moment they read. See Page numbers in an ebook, and why there are none.
A dead index is worse than no index
Leave the index out and a reader searches instead. They find what they were after or they do not, and nobody blames the book.
Ship a list of page numbers into a file with no pages and you have built something that advertises itself as a working tool and then fails in the reader's hand. They open the index because the contents lists it, find the entry they want, read "tariffs, 143, 156–159", and have nothing to do with it. Every number is inert. The conclusion they draw is that the edition was assembled without anyone looking at it, and on that point they are correct.
Three options, honestly ranked
Build a linked index. Each entry becomes a link that jumps to the place in the text it refers to. This is the real answer, and it is genuinely useful — it preserves the thing an index does that search cannot, which is point at subjects rather than at words. It is also more work than the print index was. Every entry needs an anchor at the exact sentence it means, subentries included; one printed page can hold four distinct entries, so "page 143" has to be resolved into which of the four. Page ranges lose something too: "156–159" becomes a single link to where the discussion starts, and the reader can no longer see that four pages of it are coming.
Let the reader search. Every reading system has full-text search, it is one tap, and it handles a single term well — a name, a place, a technical word. It handles concepts badly, for the same reason an automatic index does: a chapter that argues about inherited wealth for nine pages without using the phrase is invisible to it. It is also what most readers do first, in books that have an index and books that do not.
Leave it out, and say so. Let the contents and search carry it. If the print edition is indexed and the ebook is not, put one line in the front matter and one in the listing description. The reader who needs the index buys the paperback instead of reviewing the one you did not build.
Which one your book needs
Reference and academic books need the linked index. These are consulted rather than read, the index is part of the apparatus, and readers in these fields notice its absence. Budget the work. See Publishing a thesis or an academic book, and Field guides and reference layout for how a book meant to be opened in the middle is built in the first place.
General nonfiction usually does not. A memoir, a narrative history, a business book read once on a train — a detailed contents page and search serve the ebook edition. Does your nonfiction book need an index? has the same question asked earlier, for print.
A novel never had one. Nothing to decide.
In the Interior Formatter. It generates the EPUB's contents from your real chapter structure rather than from a page you typed, numbers the chapters, and carries ARIA roles and a declared language into the file — so the navigation most readers actually use is built from the book itself, whatever you decide about the index. Start your ebook → · about the Interior Formatter
Cross-references have the same disease
"See page 143" is broken in the ebook and the reader cannot act on it. So is "the table on page 88" and "the figure opposite".
Two fixes, and you can use both. Reference by structure — "see chapter nine", "see the section on paper weight", "Table 4" — which is true in the print edition as well, so one sentence serves both books. Scripture and the classics settled this centuries ago by numbering the text itself rather than the page, which is why they cite cleanly in any edition; Numbered verses and structured texts covers setting a book that way. Or make it a link, which is better where the reference is to one specific place; Links in an ebook, and where they should point covers building them so they survive a revision.
Do it in the manuscript, while you are still writing sentences. A cross-reference written as structure never needs converting.
Decide this before the index is built
An index built on page numbers cannot be converted into a linked one afterwards. The number records where the type happened to fall, not which sentence the indexer meant, and recovering that means going back to the text entry by entry and deciding again. That is not a conversion; it is building the index a second time.
So the decision comes first. If the ebook is getting a linked index, the work is planned around anchoring points in the text rather than reading numbers off proofs, and both editions come out of the same pass. If it is not, you have saved yourself a bill.
There is a separate mechanism for carrying a map of the print edition's page boundaries inside an ebook. Support varies by store and by reading system, so do not assume it and do not promise it in your description — ask the distributor you publish through.
What readers navigate with instead
The contents. In print it is a courtesy; in an ebook it is the navigation, and the device builds its own menu from the same structure. Give your sections real headings and number your chapters, and the book is findable without an index at all. See Navigation and reading order in an ebook.
If the difficulty in your book is vocabulary rather than subject, a glossary answers the question the reader actually has, and works identically in both editions. See Glossaries, appendices and other back matter.
Make your ebook
The tools are free to use: bring your manuscript once and get both a print PDF and an EPUB out of the same source, so the two editions cannot drift apart. You only pay when you want the files without the preview watermark.
Next: Tables, code and technical content in an ebook · More: Footnotes, endnotes and the reader's patience · Checking an ebook before you publish it