A book is a physical container for literature. The oral account (word of mouth, tradition, hearsay) is the oldest carrier of messages and stories. When writing Systems were invented in ancient civilizations, clay tablets or palimpsest scrolls were used, see for example the library of Alexandria. The handwritten codex, a bound book with pages and a spine, of pretty much its present form was invented in the middle ages (or earlier? Some have said that Julius Caesar invented the first codex during the Gallic Wars. He would issue scrolls folded up accordion style--like old computer print-outs might look--and use the "pages" as reference points), and was the random access memory of its time. The first books used expensive parchment or vellum (calf skin) for the pages. The introduction of paper made books less expensive, but it was not until Johann Gutenberg invented the printing press in the 15th century that books started to be affordable. The following centuries were spent on improving both the printing press and the conditions for freedom of the press through the gradual relaxation of restrictive laws. All books of the world are said to constitute the Gutenberg Galaxy, or, to use a term coined by eBook author Rick Sutcliffe in the early 1980's, the Metalibrary (see http://www.metalibrary.ws).
In the mid 19th century, paper made from pulp (cellulose, wood) was introduced because it was cheaper than cloth-based paper (term?). However, this pulp paper contained acid that causes a sort of slow fires that eventually destroys the paper from within. Libraries today have to consider mass deacidification of their older collections. Books printed 1850--1950 are at risk; more recent books have better paper.
Maintaining a library used to be the privilege of princes, wealthy people, and universities. The growth of a public library system started in the late 19th century and was much helped by donations from Andrew Carnegie.
Throughout the 20th century, libraries have faced an ever increasing rate of publishing, sometimes called an information explosion. The advent of electronic publishing and the Internet means that much new information is not printed in books, but made available online, on CDROM, or in the form of ebooks (electronic books). This does not necessarily make life easier for libraries, and so far has not resulted in any decline in the rate of paper publishing.
There have also been new developments in the process of publishing books. Technologies such as print on demand have made it easier for less known authors to make their work available to a larger audience.