The existence of boundary layers, having properties different from the bulk, influences considerably the ordering properties of thin films of condensed matter. First, we will review the problem of size effects in superconducting as well as in superfluid helium films. Liquid crystals films offer another class of ordered systems in which similar concepts can be applied. The physicochemical understanding of the boundary effects (role of the elastic distortion and of the interfacial chemical energy) and the bulk ordering mechanisms will be discussed and the analogies with the previous low temperature examples studied in the framework of the Landau model of phase transitions. A direct approach of the dynamic behavior is also possible due to macroscopic relaxation times.