The tri-arylmethanes belong to one of the most important and oldest synthetic organic dye classes. Its members include species with brilliant yellow, red, violet, blue and green hues. The tri-arylmethanes can be divided in four main groups: the hydroxys, the aminohydroxys, the diamines (the so-called Malachite series) and the triamines (the so-called Rosaniline series). Only the dyes of the diamine and triamine classes are of real importance in the textile industry. The basic structure consists of three phenyl groups linked by a central carbon atom. In this chapter the two most famous members of the Rosaniline series, namely Fuchsine and Methyl violet, will be discussed.