Presented by Zilin Chen: In the development of electron microscopy, many studies have been made to improve the resolving power. The major obstacles including spherical aberration and chromatic aberration caused by electromagnetic lenses are mostly solved. However, the information limit is still not been achieved. Decoherence phenomena are now been considered as one of the probable facts preventing better resolution. Here we reviewed some works on studying decoherence in electron microscopy. These works studied different mechanisms inside the electron optical column or on the specimen including electronic excitation, transition radiation, thermal difuse scattering, bremsstrahlung, aloof beam electronic excitation. In the free-fall electron experiment, the free-fall column also has electromagnetic components and metal tubes that might cause decoherence.