Retrieving aerosol size distributions from ground measurements is an ill-posed problem. Several methods have been developed to "regularize" it, giving a stable approximation of its solution. The aim of this paper is to review the techniques usually adopted and present some new approaches. The case of solutions retrieved both in their parametric and non-parametric form is considered. For all the considered methods the problem of choosing an optimal level of regularization is also discussed. Finally, numerical results comparing some inversion techniques in a real case are presented.