Carotenoids are widely used in food applications. Their highly unsaturated nature makes them susceptible to degradation by oxidation and thermal processes, especially under severe processing and storage conditions. The mechanisms during auto-, photo-catalyzed and photosensitized-oxidations of trans β-carotene are discussed. The oxidation products formed are mixture of epoxides, apocarotenal and hydroxy compounds. Isomerization, oxidation and breakdown of the carotenoid molecule occur as a result of thermal degradation. Two types of thermal degradation products are formed: volatile and non-volatile. The volatile fraction consists of low molecular weight molecules which vapourizes. The non-volatile fraction is the residual fraction after vapourization of the volatile fraction. The mechanisms for formation of the two fractions are discussed.