A fascinating, in-depth history of the index, with a few diversions into relevant subjects like the invention and adoption of alphabetical order and page numbers. 

Its clear the author's main interest lies with the medieval, as that's where we spend the most time. I think the time was well spent, though I'd have liked to spend a bit more time in the early 20th century on reference indexes used by librarians and their evolution into databases like JSTOR and Pro Quest. 

Overall it's an enjoyable and engaging book despite some meandering. I have a whole new appreciation for the humble index!