  Collisions are one of the key processes shaping planetary systems. Asteroid
families are outcomes of such collisions still identifiable across our solar
system. The families provide a unique view of catastrophic disruption phenomena
and have been in the focus of planetary scientists for more than a century.
Most of them are located in the main belt, a ring of asteroids between Mars and
Jupiter. Here we review the basic properties of the families, discuss some
recent advances, and anticipate future challenges. This review pays more
attention to dynamic aspects such as family identification, age determination,
and long-term evolution. The text, however, goes beyond that. Especially, we
cover the details of young families that see the major advances in the last
years, and we anticipate it will develop even faster in the future. We also
discuss the relevance of asteroid families for water-ice content in the
asteroid belt and our current knowledge on links between families and main-belt
comets.
