This review is concerned with the structure and properties of liquid crystals. We do not discuss lyotropic systems, but only thermotropic liquid crystalline mesophases. Classification, identification method, and structural characteristics of thermotropic liquid crystals are described. Fundamental physical properties such as order parameter, dielectric anisotropy, birefringence and so on are also explained. The relation between molecular structure and liquid crystalline properties is discussed in detail. We showed that the examination of the mesomorphic behavior for the compounds incorporating an angular linkage is important for the study of the relation. The relation between molecular structure and the different physical properties is also reviewed.