AbstractA survey is provided which demonstrates the synthetic importance and variety of industrial applications that have developed for ring‐opening polymerization. The number of polymers produced this way is quite significant and includes the epoxides such as ethylene and propylene oxide and other cyclic ethers such as trioxane, tetrahydrofuran and the epoxy resins. Other important systems include the polylactams such as polycaprolactam (Nylon 6), the siloxane or silicone materials, polycaprolactone, and cycloolefins such as polynorbornene. Polyoxazolines are newer monomers which can be polymerized via cationic mechanisms to yield either hydrophilic or hydrophobic tertiary polyamides. Thus, the importance of the field is quite well established and continues to grow. Major applications in coatings, fibers, elastomers, adhesives, thermoplastics and thermosets, such as in composite matrix resins, have been develope