Published online by Cambridge University Press: 14 August 2015
A review of modern concepts of the evolution of cometary orbits for the time span of some million years is presented. These concepts are based on the hypothesis of the existence of the Oort cloud, the theory of diffusion developed by Shtejns, and the work by Kazimirchak-Polonskaya concerning the influence of the major planets in transforming cometary orbits. All these ideas are currently being developed with the aid of rigorous mathematical methods by cometary researchers in various parts of the world.