Publisher Summary Terpenes are widely spread in nature, mainly in plants as constituents of essential oils. Some terpenes are pure hydrocarbons, but there are also terpenes with hydroxyl functions and carbonyl functions. Terpenes provide plants and flowers fragrance. Terpenes and related monomers are relatively nontoxic liquids that may be obtained from natural renewable nonpetroleum sources. The structure of terpenes can be essentially derived from isoprene. Crude resin is obtained by tapping living pine trees. It is a thick, sticky but still a fluid material. Because of occluded moisture, the material is milky-gray in color. A resin contains a certain amount of forest debris, such as pine needles, insects, etc. The separation of the resin into its component parts, namely rosin and turpentine, involves two basic operations: cleaning and distillation. The approximate composition of crude resin, as it is received at the plant for processing, is 70% rosin, 15% turpentine, and 15% debris and water. Low molecular weight terpene resins have an excellent solubility in elastomers. This makes them useful for adhesives. Only three terpenes, i.e., α-pinene, β-pinene, and limonene have found commercial application in the manufacture of polyterpene resins. Polyterpene resins are used as pressure-sensitive adhesives, hot-melt adhesives, and sealants. Some polyterpene resins are used in chewing gum.