Abstract
Liquid crystals are well characterized by the orientational order parameter. In most cases, the orientational order parameter of nematic liquid crystals is uniaxial and is expressed by a traceless symmetric tensor of rank two. We have developed a phenomenological theory whose starting point is the free energy expanded in powers of the orientational order parameter. By introducing the surface energy, several phenomena, including wall effects, can be explained in a unified manner. Hydrodynamic phenomena are also discussed.