Sam Leigh in The Guardian:

It would be a cliche to say that indexers are the unsung heroes of the publishing world. But unsung they generally are: no indexer usually expects or receives credit by name in books where everyone from the font designer to the snapper of the author photograph tends to get a solemn shout-out. And heroes they are, too: the index is, in any nonfiction book, more useful than almost anything else in the apparatus. It is a map of the text; a cunningly devised series of magical shortcuts that can in the good case save a scholar many hours of work, and in the bad one save a bookshop-browsing cabinet minister from having to buy a former colleague’s memoirs.