Macroporous copolymer networks form as a result of the phase separation during the free-radical crosslinking copolymerization of vinyl and divinyl monomers in the presence of an inert diluent. In this article, the develop- ments achieved in the field of macroporous networks over the last few years are presented. Special attention is paid to the preparation techniques of macroporous networks in an effort to highlight the new synthesis strategies developed in the recent years. It has been demonstrated that a variety of porous structures can be obtained during or after the cross linking process by changing the independent variable of the network synthesis, i.e. the extent of the polymer-(diluent 1 monomer) interactions, the amount of the crosslinker and the diluent as well as the initiator concentration or the polymerization temperature. The reaction system leading to macroporous networks is a (quasi)ternary system composed of a polymer network, soluble polymers, and low molecular compound (monomers and diluent). All concentrations and properties of the components of the system change continuously during the crosslinking process. It will be shown that the theoretical models developed recently correctly predict the phase separation condition during the crosslinking process as well as the total porosity of the resulting macroporous networks. q 2000 Elsevier Science Ltd. All rights reserved.