A three-piece case has a case cover made out of three pieces of covering material. Most cases are made from a single piece of cloth: see Casemaking. Nowadays the three-piece case has become something of a requirement for trade books.

I suppose it all started as a way of making the product look fancier, while slyly saving cost. Go back forty or fifty years and you’ll find three-piece cases made from two side panels of paper with a spine of cloth in order to provide strength at a shelved book’s weak point, the top of the spine by which it’s always being pulled out. Before that you’d find books with sides made of a cheaper cloth while the spine remained in a stout Buckram cloth: you’d often meet with this style of binding in the world of law books. Go even further back of course and it’s leather we are talking about — see Half bound. With leather you can see how avoiding its use on the side panels would represent a saving. Same with book cloth which costs more than paper though not of course as much as leather. 

Now we’ve arrived at a somewhat cynical spot where we have abandoned any pretense at strengthening the spine panel: we are using paper on the sides and on the spine. Might as well, as far as strength goes, just use one bit of paper rather than three. There’s a set up cost to make a three-piece case, so by putting a paper three-piece case on a book you are raising your total cost as against a one-piece paper case. Now of course the reason for doing things this way no longer has anything to do with strengthening the binding while saving cost. The motivation now is entirely directed toward getting to a “look” which we’ve lead the public to expect without spending any money to do so: it’s all about aesthetics and economy.

Here’s a step to the ultimate logic on three-piece cases — though this is by no means the first book ever to be done this way, but this is a timely one. The Consolation of Nature is a beautiful book about this year’s glorious spring in England (photographed here at the start of autumn in New York). It’s written in diary form by three naturalists living in different parts of southern England. Quite a striking story.

Here you get the look of a three-piece case without having to construct it: it’s all done with ink. That green spine is just part of the print image on the case cover. (The cost of printing the case cover is compensated for by avoiding having to print a jacket.)