A incredible book about mountaineering, written by The Mountaineers. More or less the Bible for those who wish to learn the art of mountaineering. It deals with knots for climbers (of all flavors), hikers, and mounatineers alike. It tells you how to build snow caves, what gear to buy for what type of climbing you are doing, and basically most anything that you'd like to know about climbing is in this book.
The book is now in its 6th edition. My father had it when he was a kid and now I own it as well. If you're thinking about begining climbing or mountaineering seriously, this is a book that is a must have. It goes into all of the basics and then also into many specifics about the different styles of climbing.
John Long is another author of many books that are also very useful.