The work directed toward the syntheses of thermally stable organic polymers which has been carried out in this laboratory over the past few years is reviewed. The syntheses of polyaromatic five-membered hetero-cycles obtained from the 1,3 dipolar addition reactions of disyndones and dinitrilimines, obtained from both hydrazide chloride and tetrazole precursors, show that the tetrazole monomer produces the highest-molecular-weight polypyrazole. All the polypyrazoles have good thermal stability. The 1,4 cyclo-addition reactions of bis-tstracyclones with diacetylenes afford high-molecular-weight phenylated polyphenylenes which are colorless, amorphous, and soluble in common organic solvents and have excellent thermal stability. Dipyrones are not as suitable double dienes as the bis-tetracyclones, since high-molecular-weight polyphenylenes are not obtained. The syntheses of high-molecular-weight linear poly-quinoxalines by the reaction of some bis-glyoxals with aromatic bis-o-diamines lead to thermally stable materials. By the condensation of suitable tetraketones connected by aromatic rings with the appropriate aromatic tetraamines, ladder polyquinoxalines with extremely good thermal stability can be obtained.