Liquid Crystals are partially ordered system without a rigid, long ranged structure, are beautiful and mysterious. In symmetry and structure, they are intermediate between the solid crystalline state and isotropic liquid state. The study of liquid crystalline materials covers a wide area: chemical structure, physical properties and technical applications. Due to their dual nature - anisotropic physical properties of solids and rheological properties and easy response to external perturbations (electric field, magnetic field etc.), liquid crystals are of greatest potential of scientific and technological applications. The subject of liquid crystal, in its experimental aspect, has come of age and has achieved the status of being a very exciting interdisciplinary field of scientific and industrial research. However, theoretical understanding falls far behind and is awaited to answer many basic questions. In the present monograph we addressed some of these problems within the framework of Landau de Gennes formulation and by using the unified molecular theory based on weighted density functional approach.