The Book of Shadows is a witches tome for holding spells, potion recipes, and information that can come in useful later, such as demon profiles and how to vanquish them. The Halliwell Book of Shadows is considered to be one of the most powerful known. The Charmed Ones' book was started by Melinda Warren, with the year "1693" written on it's cover page. Although it was fairly small then, each succeeding generation of Warren witches had added onto it, particularly information on demons,but also on other magical items. One of the earliest entries that was around when Melinda was alive included a curse.The book of shadows was passed down the female line of Halliwell witches.


Source: http://charmed.wikia.com/wiki/Book_of_Shadows