The catalytic activation of dioxygen continues to attract interest both due to its biological importance and synthetic potential. Metalloenzymes play crucial roles in metabolism by living organisms. The modelling of metalloenzymes by biomimetic metal complexes helps the search for useful oxidation catalysts and the understanding of their mechanisms of operation. Dioxygen is also the oxidant of choice in emission-free technologies aimed at minimising pollution of the environment, in line with the green chemistry requirements. This volume is devoted to recent progress in the field of catalytic oxidations using ruthenium, copper, iron, gold, cobalt and other complexes. Products and mechanistic aspects are given special emphasis throughout the book.