The diversity of colors found in the flora results from the interaction of a few classes of pigments with light. Betalains are nontoxic vacuolar pigments that replace anthocyanins in some families of angiosperms and some basidiomycete fungi. There are two classes of betalains: yellow betaxanthins and red betacyanins both biosynthesized from betalamic acid, a fluorescent aldehyde derivative of L-tyrosine. Betalains are found, for example, in beetroot, dragon fruit, fly agaric, bougainvillea and amaranth. In addition, the petals of yellow varieties of four-o'clock and eleven-o'clock are pigmented by fluorescent betaxanthins. In this review we discuss the major aspects of the occurrence and chemical and photophysical properties of betalains as well as some of their technological applications.