Back in mediaeval times, when people didn’t have Kindles to carry a thousand books, some book binders bound two separate books together in a single volume so that the reader had one less book to carry. In those days, reading wasn’t a very popular past time and the only books the majority of the populace read were religious in nature. Two books that were frequently bound together were the New Testament and the Book of Psalms, because both were needed during church services. They became very common in England in the first half of the 17th century.
As you can see, it has a very unusual kind of binding. The two separate books are bound such that the fore edge of one is adjacent to the spine of the other, and both books share a common back cover sandwiched between the two. When you place such a book on a shelf, the spine of one book faces outwards and the spine of the other faces inwards towards the shelf back. This odd binding style is known as dos-à-dos, a French word meaning “back-to-back”.
Some book binders took the style a bit further. The image below shows a dos-à-dos binding from 1736 featuring no less than five books.
Modern dos-à-dos bindings are rare to come by, but a different type of back-to-back binding made brief resurgence in the middle of the 20th century. These books have no back cover, but instead have two front covers that open from either end, and a single spine. The text of both books are rotated 180° relative to the other, such that when one text runs head-to-tail, the other runs tail-to-head. When a reader finishes reading one book, they have to flip the book upside down to read the second book. This is why these volumes are referred to as “upside-down books”. The correct term for such type of binding is tête-bêche, again from the French meaning “head-to-toe”, but dos-à-dos has become a blanket phrase for all kinds of two-in-one bindings.
A prime example of head-to-toe binding are the Ace Doubles series produced by the American company Ace Books in the 1950s. Ace was a science fiction publisher who placed two novels into a single volume in an attractive and affordable tête-bêche format. The Doubles were published until 1978.
A modern tête-bêche published by Ace Books.
Before we go, let’s take a look at this complicated specimen bound in the late 16th century. It contains six books—all devotional texts printed in Germany during the 1550s and 1570s—hidden inside a single binding. The book can be opened from all the four edges in six different ways.
Sources: Wikipedia / Erik Kwakkel / Abe Books