This review paper devoted to the investigation of physical properties and application of low molar mass calamatic thermotropic cholesteric liquid crystals. In chapter 1 are considered general properties of cholesterics. In chapter 2 are considered temperature dependence of the pitch in cholesteric liquid crystals. In chapter 3 are presented the electroptics and in chapter 4 photooptics in cholesterics. Chapter 5 devoted to different application of cholesterics: 5.1. Light modulators; 5.2 UV detectors; 5.3. Cholesteric liquid crystals in Dye Lasers; 5.4. Luminescent displays and light induced permanent gratings in dye doped cholesteric liquid crystals.