AbstractSince the beginning of the XVIIth century, rings of dispersed matter play an important role in theories accounting for the origin of the solar system and proto-planetary nebulae. Planetary rings afford a good opportunity of studying some of the accretion mechanisms which operate during the early evolution of a proto-planetary nebula. Three new planetary rings have been recently discovered. Space and ground-based observations have completely renewed our image of ring systems.

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... ly, a wealth of theoretical and numerical models have flourished. Collisions between ring's particles and gravitational perturbations of nearby satellites should explain most of the ring's structures. However, important questions are still unanswered. We do not understand why the rings are so dissimilar. We do not know the ring's origin and their stability over billions of years. Most of the ring's complex structures, the existence of arcs, and color and optical depth variations are not explained. Confinement mechanisms, which are so important in cosmogony, seem to be at work in planetary rings today.