Essential oils are simply the volatile oils of plants. These are concentrated liquids contain many terpenes, alkaloids and alcohols etc. Various compounds of essential oils have bioactive properties such as antimicrobial, anti-cancer, anti-diabetic, anti-viral and anti-fungal etc. This book describes the sources of essential oils, extraction and production method, characterizing tools, bioactivity, and various applications in the field of industries, daily usage, agriculture, health, and food.