Jeff N. Cuzzi, Joseph A. Burns, Sébastien Charnoz, Roger N. Clark, Josh E. Colwell, Luke Dones, Larry W. Esposito, Gianrico Filacchione, Richard G. French, Matthew M. Hedman, Sascha Kempf, Essam A. Marouf, Carl D. Murray, Phillip D. Nicholson, Carolyn C. Porco, Jürgen Schmidt, Mark R. Showalter, Linda J. Spilker, Joseph N. Spitale, Ralf Srama, Miodrag Sremcević, Matthew Steven Tiscareno, John Weiss

• We review our understanding of Saturn's rings after nearly 6 years of observations by the Cassini spacecraft. Saturn's rings are composed mostly of water ice but also contain an undetermined reddish contaminant. The rings exhibit a range of structure across many spatial scales; some of this involves the interplay of the fluid nature and the self-gravity of innumerable orbiting centimeter- to meter-sized particles, and the effects of several peripheral and embedded moonlets, but much remains unexplained. A few aspects of ring structure change on time scales as short as days. It remains unclear whether the vigorous evolutionary processes to which the rings are subject imply a much younger age than that of the solar system. Processes on view at Saturn have parallels in circumstellar disks.