Olefin Metathesis is one of the most important reactions in synthetic chemistry. This powerful synthetic tool renders accessible complex molecules that are very tedious to synthesize using traditional organic synthetic methods. As a testimony to its importance, metathesis reactions are now employed to access fine chemicals, biologically active compounds, new functionalized materials, and various polymers. In this video we focus our attention on ruthenium indenylidene complexes and show their use in the ring-opening metathesis polymerization (ROMP) of dicyclopentadiene.