Polymerized or copolymerized cyclic imino ether monomers are classified into monomers having the —NC—O— group in the ring (cyclic endo‐imino compounds) and cyclic monomers having an exo‐imino group. The polymerization of cyclic imino ethers is reviewed, as well as the chemistry of 2‐oxazolines and 5,6‐dihydro‐4
H
‐1,3‐oxazines.