The index can be in indented format with each subentry appearing on a separate line. For example:

dogs

breed clubs, 242–48

breeding of, 180–95

herding group, 135–42

Alternatively, the index can be set in run-in, or paragraph, style, in which subentries are separated by punctuation rather than line breaks. For example:

dogs: breed clubs, 242–48; breeding of, 180–95; herding group, 135–42

The indented style is easier to read and allows for greater detail in indexing. The main advantage of the run-in style is that it saves space.

There are two main choices here: letter-by-letter sort or word-by-word sort. These two styles differ in the way they treat nonalphabetic characters. In a letter-by-letter sort, spaces, commas, hyphens, and other nonletters are ignored, whereas in word-by-word sort they have their own sorting value. For example, here is a list of terms sorted letter by letter:

Newark

New Hampshire

New Jersey

Newton

New York

In a word-by-word sort, the same terms would appear in a different order:

New Hampshire

New Jersey

New York

Newark

Newton

Depending upon the type of material being indexed, the choice of alphabetization principle can significantly affect the readability of the index. An index that contains large clusters of similarly spelled names can usually be searched more quickly if alphabetized word by word. (Compare the cohesive appearance of the word-by-word example to the scattered look of the letter-by-letter sort.) Nevertheless, most dictionaries and encyclopedias use letter-by-letter sorting, so if there are no special considerations, a letter-by-letter format is likely to be more familiar to the reader. It is also the preferred style of The Chicago Manual of Style, which sets standards for most indexers.

Subentries always appear in lowercase. Main entries can be formatted in initial caps or can be kept lowercase. There are no special considerations in choosing one style over the other. Today lowercase is often preferred, capitalizing only proper nouns and adjectives.

The default setting on our computer software separates page locators from the text entry with a comma. Cross-references are preceded by a period. In run-in style the main entry is followed by a colon to distinguish it from the subentries, and all subentries are separated by a semicolon. Any of these settings can be modified to fit client preferences. For example, some publishers prefer two spaces instead of a comma to separate page locators from text.

Cross-references are usually introduced by See or See also. Some publishers use initial caps for these words, others prefer lowercase. In an indented index, the cross-references can follow immediately after the main entry or they can appear at the end, after all subentries have been listed. Thus:

dogs. See also American Kennel Club

breed clubs, 242–48

herding group, 135–42

hound group, 67–72

or

dogs

breed clubs, 242–48

herding group, 135–42

hound group, 67–72.

See also American Kennel Club

In a run-in-style index, it is preferable for cross-references to come at the end.

dogs: breed clubs, 242–48; herding group, 135–42; hound group, 67–72. See also American Kennel Club

In some indexes, special typography can make information more accessible. For example, the key terms of an index can be styled in bold for quick selection. Usually, however, special typography is applied only to page locators. Some publishers request that boldface page numbers be used for the main discussion of a topic. If a book contains a great deal of illustrative material, it might be necessary to distinguish illustrations from text references. This is often done by styling page locators for illustrations in italics. Where there is greater complexity and variety of illustrations, material contained in figures, tables, or maps can be distinguished by italicized letters f, t, and m after page numbers. Footnotes and endnotes are usually indicated by an italicized n after the page number. In some cases the number of the note is given also, as in 230n12.