An overview of the new approach to the Brownian coagulation theory developed in the author's previous papers, is presented. The traditional diffusion approach is critically analysed and shown to be valid only in the particular case of coalescence of small particles with large ones, R(1) << R(2). It is shown that coalescence of comparable size particles occurs in the kinetic regime, realised under condition of homogeneous spatial distribution of particles, in the two modes, continuum and free molecular. However, the expression for the collision frequency function in the continuum mode of the kinetic regime formally coincides with the standard expression derived in the diffusion regime for the particular case of large and small particles. Transition from the continuum to the free molecular mode can be described by the interpolation expression derived within the new analytical approach with fitting parameters that can be specified numerically, avoiding semi-empirical assumptions of the traditional models. (C) 2010 Elsevier Ltd. All rights reserved.