The various reactions catalyzed by mononuclear ruthenium complexes are reviewed through 2008. The reactions discussed are hydrogenation with dihydrogen of carbon–carbon multiple bonds and carbon–heteroatom bonds, hydrogenation via hydrogen transfer, oxidation of carbon–heteroatom bonds, oxidation of carbon–carbon bonds, oxidation of alkanes, nucleophilic addition to alkynes, reactions involving C–H activation, olefin metathesis, reactions involving allyl ruthenium intermediates, and a brief discussion of radical reactions involving mononuclear ruthenium complexes. The article attempts to emphasize the use of chiral auxiliaries for obtaining enantiospecific transformations and the impact of ligand structure on the mechanistic aspects of a particular transformation. The article is not intended to be comprehensive but tries to survey the range of organic transformations currently employing mononuclear ruthenium reactions. More than half of the references are from the past 10 years.