Indexing A-Z from The Chicago Manual of Style--the undisputed authority for style, usage, and grammar.
In this age of searchable text, the need for an index made with human input is sometimes questioned. But a good index can do what a plain search cannot: It gathers all the substantive terms and subjects of the work, sorts them alphabetically, provides cross-references to and from related terms, and includes specific page numbers or other locators or, for electronic formats, direct links to the text. This painstaking intellectual labor serves readers of any longer work, whether it is searchable or not. For searchable texts, an index provides insurance against fruitless queries and unintended results. In a word, a good index makes the text more accessible.