During the last 15 years, the area of well-defined metathesis initiator systems was characterized by almost dramatic improvements in terms of initiator activity, stability, and selectivity. In due consequence, control over polymer properties increased and metathesis-based polymerization techniques (in particular ring-opening metathesis polymerization, ROMP) have been adapted for materials science purposes. Quite recently, metathesis-based supports have entered the fields of heterogeneous catalysis as well as separation and life sciences. In this review, both the synthesis and properties of metathesis-based well-defined catalytic supports and separations systems shall be summarized. Special consideration will be given to the particular structural features that have been made possible using ROMP. (C) 2002 Elsevier Science B.V. All rights reserved.