Publisher Summary Polyamides are crystalline polymers typically produced by the condensation of a diacid and a diamine. There are several types of polyamides, and each type is often described by a number, such as nylon 66 or polyamide 66 (PA 66). The numeric suffixes refer to the number of carbon atoms present in the molecular structures of the amine and acid, respectively (or a single suffix if the amine and acid groups are part of the same molecule). The -COOH acid group reacts with the -NH2 amine group to form the amide. A molecule of water is given off as the nylon polymer is formed. The properties of the polymer are determined by the R and R' groups in the monomers. The structures of diamine monomers the diacid monomers are shown in this chapter with the help of figures. These structures show only the functional groups; the CH2 connecting groups are implied at the bond intersections. All polyamides tend to absorb moisture, which can affect their properties. Properties are often reported as DAM (dry as molded) or conditioned. The absorbed water tends to act like a plasticizer and can have a significant effect on the plastics properties. Nylon 6, nylon 11, nylon 12, nylon 46, nylon 66, nylon 610, nylon 612, nylon 666, amorphous nylon, and semicrystalline polyamide (PACM 12) are also discussed in the chapter. Polyphthalamide/high performance polyamide (PPA) as a member of the nylon family is a semicrystalline material made from a diacid and a diamine. Another partially aromatic high-performance polyamide is polyarylamide (PAA).