An essential oil is a class of volatile oils that give plants their characteristic odor. Essential oils are also known as ethereal oil, volatile oil, aetherolea or, simply, as the oil of the plant from which they are extracted, for example, oil of clove. The oil is essential in the sense that it contains the essence of vegetal specie fragrance, the characteristic fragrance of the plant from which it is derived. These can be extracted from different parts of plants, for example, stems, leaves, and flowers. Plants provide the inspiration and foundation for modern medicines. Natural product isolation is a key compo- nent of the process of drug discovery from plants. The relationship between organic chemistry and biochemistry is introduced.