U. S. Schwarz Phase behavior of amphiphilic systems Acta Phys. Pol. B 29: 1815-1825 (1998) Due to the enormous complexity of amphiphilic systems on microscopic scales, their modelling often starts from mesoscopic length scales. In recent years Ginzburg-Landau theories and curvature models have fostered considerable progress in understanding different aspects of binary and ternary amphiphilic systems. We have investigated to what extent these models can be used to understand amphiphilic phase behavior. It is argued that Ginzburg-Landau model are well suited to describe ordered phases at low temperatures. A Ginzburg-Landau model for binary amphiphilic systems is presented which yields the typical phase sequence disordered micellar - micellar cubic - hexagonal - lamellar - bicontinuous cubic - reversed hexagonal - reversed micellar cubic - disordered reversed micellar, which is observed experimentally. At higher temperatures fluctuation effects become more important, and lamellar and sponge phases/microemulsions are favored. It is argued that curvature models which include fluctuation effects and long ranged interactions like steric or van der Waals interations are more suited to predict amphiphilic phase behavior in this case. It is shown that such a model can explain, for example, that in ternary systems the lamellar phase often extends far into the water apex when the phase inversion temperature is approached from below.