How to make an index in Word: mark the entries, insert the field, and the three things that break it

An index in Microsoft Word is built in two steps that are easy to confuse. First you mark the words you want indexed, which puts a hidden field next to each one in the text. Then you insert the index itself, which reads those fields and builds the list with page numbers. Nothing appears until the second step, and nothing updates on its own after it, which between them explain almost every complaint about Word indexes. The whole job on a long document is an afternoon, and most of that afternoon is deciding what deserves an entry.

An index is not a table of contents. A table of contents is built from your headings and lists the document's structure in order. An index is built from terms you choose and lists them alphabetically with every page they appear on. A long document often wants both, and they are made in completely different ways.

Step one: mark the entries

• Select the word or phrase in the text.
• Press Alt and Shift and X together, which opens the Mark Index Entry box. The same box lives on the References tab under Mark Entry.
• Check the main entry text. Word fills it with what you selected, and you can change it. This is how you index a plural under its singular, or a brand under a category.
• Add a subentry if the term needs one. Typing a subentry produces the indented second level you see in a book index.
• Choose Mark, or Mark All. Mark tags this one instance. Mark All tags every exact match in the document, which is the right default for a term that matters and the wrong one for a common word.
• Carry on without closing the box. It stays open, so you can click into the document, select the next term and mark it. This is the part that goes quickly once you stop closing it.

Marking inserts a hidden field next to the word, which looks like a brace with XE and your entry text inside it. Those fields are formatting marks rather than text: they do not print, and they appear on screen only while formatting marks are shown.

Step two: insert the index

• Put the cursor where the index goes, which is usually the last page. Insert a page break first so it starts cleanly.
• On the References tab, choose Insert Index.
• Pick the format. Indented is the normal book style with subentries stepped in. Run-in puts subentries on the same line, which saves space and reads less easily.
• Choose one column or two. Two is conventional in print and tighter on screen.
• Decide about right aligned page numbers and a leader, which is the row of dots. Both are presentation and neither affects the entries.
• Insert it. Word reads every marked field and builds the alphabetical list with page numbers.

The shortcut for a long document

Marking three hundred terms by hand is the slow way. Word will do it from a list, using a feature called AutoMark, and the input is a two column table saved as its own Word file: the term to find on the left, the index entry to create on the right. Then, on the References tab, open Insert Index and choose AutoMark, point it at that file, and Word marks every occurrence in one pass.

Two cautions that decide whether this saves time or costs it. AutoMark marks every instance of every term, so a common word in the left column produces an index entry on fifty pages and makes the index useless. And it is case sensitive in practice, so include the capitalised and lower case forms as separate rows where both occur. Build the list from a first read of the document rather than from imagination, and keep the file: it is reusable for the next edition.

The four faults in every first attempt

What you see	Why	The fix
Strange braces and XE codes all through the text	Formatting marks are switched on. The codes are hidden fields, not text you typed	Turn formatting marks off with the paragraph symbol button on the Home tab, or Control and Shift and 8
Page numbers are wrong after editing	An index is a snapshot. It does not update itself	Click in the index and press F9, or use Update Index on the References tab. Do this last, after every other edit
The same idea appears twice, under two spellings	Entry text was typed slightly differently each time	Decide the wording once and keep a list. Fix the odd ones by editing the text inside the XE field itself
The index is empty or missing terms	Nothing was marked, or the marking happened in a different part of a document split across files	Switch formatting marks on and look for the XE fields. No fields means step one did not happen

The things worth knowing beyond the basics

• Index a range of pages, rather than one, by selecting the whole passage, bookmarking it, and then marking an entry that refers to that bookmark. This is how a book shows pages 40 to 48 for one subject.
• Add a cross reference in the Mark Index Entry box to produce a see also line pointing readers at the term you did use.
• Edit an entry by editing its field. Turn on formatting marks, find the XE code, change the text inside the quotation marks, then update the index.
• Delete an entry by selecting the whole XE field, braces included, and deleting it. Removing the word from the index itself does nothing, because the index is rebuilt from the fields.
• Mark as you write, not afterwards. On a document you are still drafting, marking terms as they arrive turns an afternoon into ten minutes spread over a week.
• Keep the entry list in the document's own front matter while you work, as a scratch list of the wording you have settled on. It is the single thing that keeps a two person index consistent.

What belongs in an index

The mechanics are the easy half. A useful index lists what a reader will look up rather than every noun in the document: the terms of art, the named processes, the people and organisations, the places, and the things somebody will want to find again without remembering which chapter held them. Three tests that cut a bloated index down. Would a reader search for this word rather than read to it. Does the entry point at a page where the term is explained rather than merely mentioned. And does the entry read as the reader would phrase it, not as the author phrased it.

For a document somebody else will maintain, the structure matters as much as the index, which is the same argument as for a reusable table of contents and for the two kinds of checklist in Word: build it from the document's own structure so the next person can update it without rebuilding it.

Questions about Word indexes

Where is the index option in Word?

On the References tab. Mark Entry marks a term, and Insert Index builds the list. On a Mac the same two commands sit in the same place on the ribbon.

Why does my index not update when I edit the document?

Because it is a field rather than live text. Click inside it and press F9, or use Update Index. Make a habit of doing it as the last action before you export a PDF.

How do I hide the XE codes?

They are formatting marks. Switch them off with the paragraph symbol on the Home tab, or Control and Shift and 8. They never print either way.

Can I index automatically from a list?

Yes, with AutoMark and a two column Word file of terms and entries. Keep common words out of the left column or the index fills with noise.

How many entries should an index have?

Enough that a reader finds what they look for and few enough that the list is scannable. For a report of thirty pages, several dozen entries is normal. For a manual, one or two entries per page of content is a reasonable target.

Does an index work in a PDF export?

Yes, with the page numbers frozen as they were when you last updated it, which is the reason to update immediately before exporting.

Should I use an index or a table of contents?

A table of contents for structure, an index for lookup. A long document benefits from both, and they are built independently of each other.

The index a reader never opens

An index exists so somebody can find the part of a long document they need. The same job now gets done without the document being opened at all: a reader asks an assistant a question and gets an answer assembled from whatever it has read, with two or three sources named. For anything a business publishes to be found that way, the useful equivalent of a good index is plain structure and terms written the way readers phrase them, which is the same discipline this page asks for in a printed one. AI Knows Us asks the buying questions customers ask across the main assistants and records which companies get named and what the answers were built from.