Selective oxidative transformation of various functional groups with environment friendly and easily accessible oxidants can be readily achieved with a proper ruthenium catalyst. Ruthenium catalysts can be very powerful tool in synthetic chemistry for selective catalysis of oxidative transformations such as asymmetric epoxidation of alkenes, generation of dioxygen species, dihydroxylation of olefins, and oxidative dehydrogenation of alcohols. Ruthenium catalysts are also widely employed in metathesis reactions, with Grubbs′ catalysts being the most well-known in the field of olefin metathesis. The wide popularity of Grubb′s catalysts can be explained by their high tolerance of various functional groups, and their high stability in air and a plethora of solvents.