During the Middle Ages there were very few books. There are a couple of reasons for this. First of all, not many people could read (the ability to read belonged to the clergy and some of the upper classes). Secondly, there were no printing presses. Everything had to be copied by hand. These were done by monks called scribes. There's a picture of one at the top of this page.
Some of these manuscripts were decorated beautifully and were works of art. Look below to see an example.