Obviously during the Medieval period, books weren't cheap and abundant like today. Prior to the Gutenberg press, they had to be painstakingly copied or written by hand. They were expensive, and rarely did any given book (other than the bible) have more than a handful of copies made, and usually at great expense. Books were sometimes rented out, for the purposes of copying.
Many books as such had to have durable covers, and often would be given ornate ones in the process (with tooled leather, inlaid stones, metal appliances, etc). Frequently they'd have latches or straps to keep them closed. Here are some examples I found with some basic googling:
