Crystalline-state polymerization yields polymers having different structures in comparison with those yielded by a conventional solution polymerization, because of the limited mobility and arrangement of monomers. Crystalline-state polymerization can be categorized into two types, topochemical polymerization and inclusion polymerization. Based on this background, we developed a new methodology to yield a polymer. In this system, a copolymerization of a host monomer and a guest monomer occurs, therefore it can be considered as a combination of topochemical polymerization with inclusion polymerization. This new polymerization enabled to control the polymerization degree in step-growth polymerization, as well as to control the shape and network structure of a network polymer. These examples are shown in this chapter.