Book excerpt: Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the oil of the plant from which they were extracted. Essential oils are generally used in perfumes, cosmetics, soaps and other products, for flavoring food and drink, and for adding scents to incense and household cleaning products. Various essential oils have been used medicinally at different periods in history. Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer, and often are based solely on historical accounts of use of essential oils for these purposes. Interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that claims that essential oils and other aromatic compounds have curative effects. Oils are volatilized or diluted in carrier oil and used in massage, diffused in the air by a nebulizer, heated over a candle flame, or burned as incense. This book describes about the physicochemical properties, chemical composition, distillation, yield, quality of essential oils, process of extraction of essential oils, manufacture of essential oils, products derived from essential oils and so on. The book in your hands contains formulae, processes, and test parameters of different types of essential oils derived from different natural sources. This is very helpful book for new entrepreneurs, professionals, institutions and for those who are already engaged in this field.