Abstract The dynamics of planetary rings are reviewed in the light of data derived from the recent spacecraft missions to the outer planets. It is shown that although the ring systems of Jupiter, Saturn, Uranus and Neptune display a great diversity of phenomena and dynamical structures, they have many features and problems in common. The role of small satellites in determining ring structure is reviewed, with particular emphasis on the ring system of Saturn. There is mounting evidence that some of the smaller satellites may have densities as low as 0.6 g cm-3. Because Saturn has examples of most of the types of rings seen elsewhere in the Solar System, the forthcoming Cassini mission has particular importance for ring dynamicists. A summary is presented of the critical ring observations that can only be made by a spacecraft orbiting Saturn for an extended period.