Solid-state, radiation-induced polymerization studies are usually conducted by bulk polymerization, followed by separation and gravimetric determination of yield in order to correlate polymerization conditions with results. Microscopical methods of studying some types of these reactions offer many advantages over conventional techniques, and, in addition, yield information not easily obtainable otherwise. Quantitative data relating polymerization rates and behavior to crystal orientation, size, polymorphism, temperature, radiation dose, inhibitors, and solid solutions of isomorphous systems can be obtained. Typical results obtained by X-radiation-induced polymerization of tributylvinylphosphonium bromide, tributylvinylphosphonium iodide, and their solid solutions are presented to illustrate the application of these techniques.