Processing of oil shale in Estonia was started in the 1920s. Since 1924 to the present time the technology of processing large-particle oil shale in vertical retorts with gaseous heat carrier, and since 1980 that of processing fine-grained oil shale with solid heat carrier are in operation. To assess the quality of oil shale the standard Fischer assay method (heating in aluminum retort to temperatures 500-520degreesC) is used For oil shales of all deposits of the world at this temperature the thermal decomposition of organic matter is completed, but practically no decomposition of the mineral portion of oil shale takes place. At commercial realization of oil shale processing the yield and the quality of products depend on many factors: oil shale particle size, methods of heat input, kind of heat carrier and its temperature, duration of retorting, and also on secondary processes which proceed inside the oil shale particle and in the interparticle space, and others. The comparison of various known technologies for processing oil shales is made, and a possible theoretical foundation of process features is given. An estimation of the impact of the process on the environment is also discussed. As a result directions for the further development of existing technologies are given.