Unlike planets and satellites, smaller bodies in the solar system, like asteroids, comets, and meteoroids, are affected by nongravitational forces due to collisions, viscosity, and in some cases electromagnetic forces. The way such forces change the orbits of the bodies seems not to have been analyzed until recently. For example, it is generally believed that collisions between asteroids will make their orbits spread over an increasing volume of space and that collisions inside meteor streams will make their cross sections increase. At least under certain conditions the reverse is true, as shown by the papers of Baxter and Trulsen at this symposium. Furthermore, besides the usual picture of meteoroids being emitted by comets, we should also discuss the reverse process; viz, comet formation by bunching in a meteor stream.