This is a very solid, comprehensive beginners guide to Aromatherapy. The book includes information about different herbs, how to use them, and how to distill oils, as well as some history on Aromatherapy. An excellent place to start if you're interested in distilling or mixing oils or better understanding the oils you're using.
If your looking for a comprehensive book on the history of aromatherapy, this is the book. This workbook walks you through the use of essential oils, covers the history, folklore, science, and the art of aromatherapy. Definite read if you have an interest in aromatherapy.