Resin, in the most specific meaning of the term, is a hydrocarbon secretion of many plants, particularly coniferous trees. It is distinct from other liquid compounds found inside plants or exuded by plants, such as sap, latex, or mucilage. More broadly, the term “resin” is also used for many thick liquids, some of them artificial polymer bases (synthetic resins), that during normal use, harden into transparent or opaque solids. Natural plant resins (the subject of this article) are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives and food glazing agents. They are also prized as an important source of raw materials for organic synthesis, and provide constituents of incense and perfume. Plant resins have a very long history that was documented in ancient Greece by Theophrastus, in ancient Rome by Pliny the Elder, and especially in the resins known as frankincense and myrrh, prized in ancient Egypt. These were highly prized substances, and required as incense in some religious rites. Amber is a hard fossilized resin from ancient trees. The word resin comes from French resine, from Latin resina “resin”, which either derives from or is a cognate of the Greek rhētinē “resin of the pine”, of unknown earlier origin, though probably non-Indo-European.