Abstract
There are many particles in the atmosphere of shapes other than the sphere. For these particles the rigorous solutions obtained from Mie theory cannot be used. The purpose of this paper is to review various approximations used in the problems of interaction of light with small particles. Rayleigh approximation, discrete dipole approximation, born approximation and finally anomalous diffration approximation are discussed starting from the Maxwell equations written in the integral form. The relations obtained from Rayleigh and Born approximations were improved in the way that the extinction cross section would be computed using the optical theorem.