Innovations in transition metal catalyzed low pressure polymerization of ethylene, 1-olefins, styrene, and cycloolefins offer new opportunities for the production of rubbers, thermoplastic elastomers and blends. As a function of the metallocene structures it is possible to control molar mass, molar mass distribution, stereo-chemistry, end groups, comonomer incorporation, long- and short-chain branching, morphology, polymer compatability, and elastomer properties. High molecular weight atactic polypropylene and stereoblock polypropylenes are available as elastomers and blend components. Metallocene catalysts produce novel families of ethylene copolymers with higher 1-olefins, e.g., 1-octene, as well as with styrene and norbornenes. New nickel- and palladium-based catalysts polymerize ethylene to afford highly branched polyethylene rubber and also elastomeric copolymers of ethylene with polar monomers such as methyl acrylate and carbon monoxide.