Figueiredo Neto and Salinas (physics, U. of Sao Paulo) note that soaps have been with us for several millennia, and that their use in washing is directly related to fundamental concepts in self- assembling and ordering. As surfactant molecules, they are partly water-soluble and partly oil-soluble. These lyotropic systems are excellent examples of polymorphism and phase transformations, depending on their temperature, pressure, and other physico-chemical parameters. The authors examine the main experimental facts and techniques of lyotropic systems, including their mesophases and applications and the basic concepts of phase transitions. They examine phase diagrams of lyotropic mixtures, phase transitions between periodically organized lytropic phases, isotropic micellar and bicontinuous phases, nematic and cholesteric phases, and the lyotropic phases in one to three dimensions. They also examine recent developments, such as microemulsions and Langmuir-Blodgett films.