Amphiphilic molecules, such as the carboxylic acids and their salts, organic esters and alcohols, lipids, phospholipids and some other organic compounds have a tendency to form a wide variety of complex supramolecular structures. These could be liquid crystalline layers, micelles, vesicles and different exotic multilayer patterns. Such properties are essential for many biological processes and industrial applications. To describe these phenomena a theoretical model is proposed based on the weighted-density functional approach. Attention is focused on ordering in surfactant films of amphiphilic compounds at the liquid-vapour and liquid-liquid interfaces. These compounds contain one or several polar groups and a hydrophobic tail, which are responsible for the different kinds of liquid-expanded-liquid-condensed and layering phase transitions in the films. Such transitions involve essential changes in the conformational or orientational states of the surfactant molecules depending on their chemical composition and stiffness. Much experimental data for π - A isotherms are consistent with the theoretical results.