Comet Hale-Bopp defines a milestone event for cometary science: it is the first really big comet observed with modern equipment on the ground and from space and due to that; it is considered the new reference object in cometary sciences.

At the beginning of a new era in spacecraft exploration of comets and five years after Hale-Bopp’s perihelion passage these proceedings of invited and contributed papers for IAU Colloquium 186 Cometary Science after Hale-Bopp review the state-of-the-art knowledge on comets, the icy, dusty and most primordial left-overs of the formation disk of our own solar system.