Forward and inverse Monte Carlo modeling of cometary dust tail and coma images has provided one of the best approaches to infer the basic physical dust parameters and their time dependence: mass loss rates, ejection velocities, and size distribution functions. These methods attempt to fit the brightness distribution found in cometary astronomical images at a variety of wavelengths. The trajectories and the light scattered by the dust particles are functions of the size parameter, shape, and refractive index. In this paper we describe briefly the Monte Carlo technique, and present some applications.