Our laboratory has a long interest in methionine (Met) biosynthesis, metabolism and its role in oxidative damage. Although the primary goal of this review was to summarize more recent studies on the role of Met oxidation in proteins on cellular function, we have used this opportunity to describe some of the early studies that elucidated the unique and important functions that Met has in one carbon metabolism, and as an initiator of protein synthesis. Oxidative damage, our main focus, is believed to be a major factor in age related diseases and the aging process. The oxidation of Met residues in proteins to methionine sulfoxide has turned out to be an important biomarker of oxidative damage since there are specific enzyme systems, methionine sulfoxide reductases, that can repair this damage and which play an important role in protecting cells against oxidative damage.