Before the printing press, copies made of books had to be hand written. This led to errors in the text, and, as copies were made of copies, more mistakes were made.
Johannes Guttenberg invented the first printing press in 1455. This made it possible for a full page to be printed at one time. The first book he printed was the Bible.
Printing press technology was brought over the Atlantic as America was colonized. One of the first books printed in this part of the world was the "Bay Psalm Book," printed by the Puritans.
There were many book publishers by the mid-1800s, which bought the price of books down. In the 1880s most books were paperbacks and cost 5 to 15 cents. This gave everyone the chance to read and own books, not just the rich.
The number of book publishers has shrunken in today's world; many of the large companies are part of media conglomerates. Many books are also published electronically through programs such as Amazon's Kindle in conjunction with the classic ink-and-paper book.