Metallocenes and other transition metal complexes, activated by methylaluminoxane allow the synthesis of polyolefins with a highly defined microstructure, tacticity, and stereoregularity. New copolymers, long chain branched polymers, and polyolefin nanocomposites are produced by these highly active catalysts. A better understanding of the structure of active sites for the olefin polymerization will lead to findings of new and simpler co-catalysts. Ethene or propene can be copolymerized with 1-olefin macromers with chain lengths up to 12,000 g mol(-1) as well as with cyclic olefins. Polypropenes of high molecular weight and filled with multi-walled carbon nanotubes show exciting new physical and mechanical properties and are prepared by in situ polymerization. These, and other polyolefin specialities, will be new future materials in a wide range of applications.