Hypercrosslinked polystyrene networks have been recognised since the 1970s. They were prepared by extensive crosslinking of linear polystyrene chains in a strongly solvating media. Generally, the basic principle of obtaining hypercrosslinked polymers consists in the formation of a rigid highly solvated three-dimensional network. Owing to the high rigidity and reduced degree of chain entanglement, such "expanded" networks are characterized by loose chain packing, i.e., high free volume, and the unique ability to swell in both good solvents and non-solvents. In addition to the above polymer-analogues transformation of polystyrene, the article expands the synthesis techniques to polymerization and polycondensation procedures and also involves other types of polymers and monomers. Typical examples of preparing hypercrosslinked networks include the crosslinking of linear chains of polysulfone and polyarylates, copolymerization of styrene with a large amount of divinylbenzene, self-condensation of p-xylylene dichloride. All resulting materials differ substantially from classical polymers of the same chemical nature and comprise a new class of hypercrosslinked polymeric materials. Some polymers described in the literature were shown to also belong to the hypercrosslinked family. (C) 2002 Published by Elsevier Science B.V.