The radical ring-opening polymerization (RROP) behavior of the following monomers is reviewed, and the possibility for application to functional materials is described: cyclic disulfide, bicyclobutane. vinylcyclopropane, vinylcyclobutane, vinyloxirane, vinylthiirane, 4-methylene-1,3-dioxolane, cyclic ketene acetal, cyclic arylsulfide, cyclic alpha -oxyacrylate, benzocyclobutene, o-xylylene dimer, exo-methylene-substituted spiro orthocarbonate, exo-methylene-substituted spiro orthoester, and vinylcyclopropanone cyclic acetal. RROP is a promising candidate for producing a wide variety of environmentally friendly functional polymers. (C) 2000 John Wiley & Sons, Inc.