Introduction. History and Sources of Essential Oil Research. Sources of Essential Oils. Natural Variability of Essential Oil Components. Production of Essential Oils. Chemistry of Essential Oils. Analysis of Essential Oils. Use of linear retention indices in GC/MS Libraries for Essential Oil Analysis. Safety Evaluation of Essential Oils. Metabolism of Terpenoids in Animal Models and Humans. Central nervous system effects of essential oil compounds. Effects of Essential Oils on Human Cognition. Aromatherapy with Essential Oils. Essential Oils in Cancer Therapy. Antimicrobial activity of selected essential oils and aroma compounds against airborne microbes. Quorum Sensing and Essential Oils. Functions of Essential Oils and Natural Volatiles in Plant-Insect Interactions. Essential Oils as Lures for Invasive Ambrosia Beetles. Adverse effects and intoxication with essential oils. Adulteration of Essential Oils. Essential Oils and Volatiles in Bryophytes. Biotransformation of Monoterpenoids by Microorganisms, Insects, and Mammals. Biotransformation of Sesquiterpenoids, Ionones, Damascones, Adamantanes, and Aromatic Compounds by Green Algae, Fungi, and Mammals. Use of Essential Oils in Agriculture. Essential Oils Used in Veterinary Medicine. Encapsulation and Other Programmed/ Sustained Release Techniques for Essential Oils and Volatile Terpenes. Essential oils as Carrier Oils. Influence of Light on Essential Oil Constituents. Influence of Air on Essential Oil Constituents. Influence of Air on Essential Oil Constituents. Industrial Uses of Essential Oils. Storage, Labeling and Transport of Essential Oils. Recent EU Legislation on Flavors and Fragrances and Its Impact on Essential Oils.