While a number of books and review articles describe the importance and application of different aspects of coupling reactions, this Handbook will be a compilation of all major catalyst components in use in the area, and is intended to guide the experimentalist and facilitate choice among the numerous reagents available for any one purpose.   The Handbook will detail pre-catalysts, catalysts, and ligands prominently employed in coupling reactions, broadly defined. Included will be catalyst systems used in Heck, Kumada-Tamao-Corriu, Suzuki-Miyaura, Hiyama-Hatanaka, Negishi, Migita-Kosugi-Stille, Buchwald-Hartwig, and Tsuji-Trost coupling reactions. The Handbook will consist of a compilation of artices taken from the EROS database, with the inclusion of about 20 newly commissioned catalysts/pre-catalysts/ligands that have made an impact in this area of synthetic organic chemistry.   The EROS series of books has focused on the most fundamental aspects of synthetic organic chemistry (e.g., oxidations, reductions, peptide coupling, fluorinated reagents, etc.). This spin-off volume follows that legacy by listing, in a single volume, those catalyst systems that have become essential for carbon-carbon and carbon-heteroatom bond-forming reactions catalyzed by transition metals. Because of the central role that these coupling processes play in modern synthetic organic chemistry, this particular volume would appear to fill a major void in the series