There is a class of reactions known as oxidation or reduction reactions that involve the gain or loss of two electrons. This chapter introduces a few oxidation reactions and the typical transformations associated with them. An oxidation is formally defined as a reaction accompanied by the loss of electrons from an atom or a group. In an oxidation reaction there are structural changes in the product relative to the starting material. These changes usually include either loss of hydrogen atoms or the replacement of a hydrogen atom bonded to carbon with a more electronegative atom, usually a heteroatom. Jones oxidation is a powerful oxidizing medium for the conversion of alcohols to ketones. The reaction of cyclohexene with osmium tetroxide gives a five-membered ring product, an osmate ester.