This article reviews the current state of art of photopolymerization of crystalline diacetylenes, although complementary information on thermal and γ-polymerization is also included whenever felt appropriate. Priority is given to an outline of recent achievements regarding reaction kinetics and energetics as well as to model considerations for both initiation and propagation of the polymer chain. It will be shown that at least for diacetylene-bis(p-toluenesulfonate) (TS) existing experimental data allow establishing a consistent picture of the polymerization process. After discussing recent works on photopolymerization in Langmuir-Blodgett-multilayer assemblies, including sensitization and self-sensitization effects, potential applications of the unusual optical, electrical, and reaction properties of diacetylenes are outlined.