Why an index? Indexers gasp with horror when good nonfiction works appear without indexes. But authors might have legitimate reasons to wonder, “Does my book really need an index?” There are, in fact, convincing reasons nonfiction works should have indexes. Potential buyers often scan indexes to decide whether to purchase a book. Researchers depend upon indexes to find and cite information in the text. Reviewers and other colleagues will assess the stature of a book based partly on the index. Sometimes reviewers comment explicitly on a good index, and it is the author who stands to gain from this praise.

Every serious book of nonfiction should have an index if it is to achieve its maximum usefulness. Chicago Manual of Style

Why not index the book myself? Clearly there are advantages to author-produced indexes. The author, after all, knows the book better than anyone. But professional indexers are trained to think like readers, not authors. Their emphasis is on providing a tool for finding information useful to someone who does not know the book. Moreover, indexing is tedious work that ties up authors' valuable time and can cause production delays for publishers. Professional indexers are trained to work efficiently and provide quick and reliable results.

I indexed my first book before I started professional indexing. It was a credible effort, but there are many things I would change as a result of later skills learned as a professional indexer. I have written an account of my experience as an author indexer for a collection on scholarly indexing. See "Confessions of an Author-Indexer," in Margie Towery and Enid L. Zafran, Indexing Specialties: Scholarly Books. Wheat Ridge, Co.: American Society of Indexers, 2005.

How much does indexing cost? Most indexers charge a per-page rate that varies depending on the size and layout of the typeset page and the substantive density of the book. That is, the per-page rate for a travel guide or grade-school textbook would be much less than for a philosophy treatise or medical reference book. This rate is agreed upon before indexing begins and is based on actual page samples or a reasonable estimate of their scope. Occasionally other reimbursement methods are used, such as hourly rates.