The term polymer encompasses a very large, broad classes of compounds, both natural and synthetic, with a wide variety of properties. Because of the extraordinary range of properties of polymeric materials, they play an essential and ubiquitous roles in everyday life, from those of familiar synthetic plastics and other materials of day-to-day work and home life, to the natural biopolymers that are fundamental to biological structure and function.

A polymer is a chemical compound or mixture of compounds consisting of repeating structural units created through a process of polymerization. The term derives from the ancient Greek word πολύς (polus, meaning "many, much") and μέρος (meros, meaning "parts"), and refers to a molecule whose structure is composed of multiple repeating units, from which originates a characteristic of high relative molecular mass and attendant properties. The units composing polymers derive, actually or conceptually, from molecules of low relative molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the modern IUPAC definition. Polymers are studied in the fields of biophysics and macromolecular science, and polymer science (which includes polymer chemistry and polymer physics).