  Debris disks are tenuous, dust-dominated disks commonly observed around stars
over a wide range of ages. Those around main sequence stars are analogous to
the Solar System's Kuiper Belt and Zodiacal light. The dust in debris disks is
believed to be continuously regenerated, originating primarily with collisions
of planetesimals. Observations of debris disks provide insight into the
evolution of planetary systems; the composition of dust, comets, and
planetesimals outside the Solar System; as well as placing constraints on the
orbital architecture and potentially the masses of exoplanets that are not
otherwise detectable. This review highlights recent advances in
multiwavelength, high-resolution scattered light and thermal imaging that have
revealed a complex and intricate diversity of structures in debris disks, and
discusses how modeling methods are evolving with the breadth and depth of the
available observations. Two rapidly advancing subfields highlighted in this
review include observations of atomic and molecular gas around main sequence
stars, and variations in emission from debris disks on very short (days to
years) timescales, providing evidence of non-steady state collisional evolution
particularly in young debris disks.
