Until now polymerization catalysis was linked to transition metal chemistry with only few exceptions. However, in our work we will show that the main group metal salt MgCl 2 can give rise to oligomerization and polymerization of olefins. Since the late 1960s MgCl 2 has been used as support material for commercial Ziegler-Natta catalysts in many variations. Although the influence of this ‘inert’ support on the structure and properties of the resulting polymers is known, investigations of the reactivity of MgCl 2 with olefins are rare. Surprisingly MgCl 2 polymerizes strained olefins like norbornene, norbornadiene, 5,6-dichloronorbornene and bistrifluoromethyltricyclo[4.2.2.0]decatriene in high yield to high molecular weight products. The polymers are characterized by FT-IR, NMR, size exclusion chromatography (GPC) and thermoanalytical methods. The properties and structure of these polymers correspond to those prepared by ring-opening metathesis polymerization (ROMP). The characterization of different MgCl 2 phases is carried out by the use of powder diffraction measurements, electron microscopy, measurements of the specific surface (BET), simultaneous thermal analysis (STA), and atomic absorption spectroscopy (AAS).