As already mentioned, the carotenoids are a class of natural pigments that is very widespread and it was demonstrated that they occur in all the three domains of life, i.e. in the eubacteria, the archea and in the eucarya. A rich source for carotenoids are the algae and more than 100 carotenoids have been isolated and characterized from these organisms. For human diet the most important source for carotenoids are plants, where often the brilliant colors of the carotenoids are masked by chlorophylls, e.g. in green vegetables. The carotenoids are responsible for the beautiful colors of many fruits (e.g. pine-apple, citrus fruits, tomatoes, paprika, rose hips) and flowers (e.g. Eschscholtzia, Narcissus), as well as the colours of many birds (e.g. flamingo, cock of rock, ibis, canary), insects (e.g. lady bird), and marine animals (e.g. crustaceans, salmon). Normally carotenoids occur in low concentrations, but this varies enormously from one source to another. The total carotenoid production in nature has been estimated at about 100’000’000 tons a year. It has been demonstrated by the analysis of serum and human breast milk that up to 50 dietary carotenoids from fruits and vegetables may be absorbed and metabolized by humans.