Healing Oils of the Bible, by David Stewart, Ph.D. This was the first book I read. I followed the protocol, on page 92, that Dr. Stewart used for his own knee wellness, and it has worked for my right knee.
Surviving When Modern Medicine Fails: A definitive guide to essential oils that could save your life during a crisis, by Dr. Scott A. Johnson. I use this book for reference almost weekly. It is well categorized, making essential oils easy to understand, and integrate into a daily lifestyle.
Essential Oils Pocket Reference, from Life Science Publishing. A small 6 inch square little book with every oil, it’s origin, and use. It comes in a larger desk size, but I find this little one meets my needs, and budget. If you are getting into oils, it really must be in your library.