The Nursing Mother's Companion is so informative, concise, well-laid out, and comprehensive that I don't know how I would have survived learning to breastfeed without it.
It answered ALL of my questions as I was trying to master nursing my baby. It has chapters that go in-depth on all subjects relating to breastfeeding as well as wonderful "Survival Guide" sections that help you quickly pinpoint problems, tell you why you're having them, and then give you solutions that actually work and work well. When you're in pain (physical or emotional) from learning such a new skill, you want answers as quickly as possible.
This book covers preparation during pregnancy, learning to breastfeed, and it continues to teach and help throughout your entire nursing experience. It has sections on special circumstances like nursing premature babies, adopted babies, and babies with conditions or diseases that make nursing difficult. It also has advise for mothers with special circumstances.
One more aspect about this book that was wonderful was it's non-preachy tone. The author asserts that breast is best (which you probably know if you're reading the book), explains why, then moves on to the practical matters of breastfeeding. No annoying and repetitive condemnation of anyone choosing to formula feed.
This is a wonderful book! I recommend it to everyone who is breastfeeding and give it as shower gifts to soon-to-be nursing moms.