The past 15 years have witnessed tremendous advances in the design and use of organometallic complexes as precatalysts for olefin polymerization. Most recently, an intense search has been started in next-generation single-site catalysts. New approaches have been taken to ligand design. This research has yielded extraordinary results such as catalysts with activities as high or higher than those of conventional metallocenes, stereospecific and living polymerizations, and amazing new polymer structures such as highly-branched ethylene homopolymers. This volume presents some of the recent disclosures in this exciting and rapidly expanding field, featuring papers by some of the leading investigators.