Summary and Recommendations

The purpose of IAU Colloquium 180 was to prepare a series of resolutions re-garding the specication of the International Celestial Reference System (ICRS) for consideration by Joint Discussion 2 at the XXIV IAU General Assembly. These resolutions provide denitions, standard algorithms, and parameters to link observable quantities with reference coordinates within the ICRS. Speci-cally recommended were denitions of the celestial intermediate pole and celes-tial ephemeris origin, an improved precession/nutation theory, and a new set of standard values for astronomical constants. These resolutions have far-reaching eects on positional and dynamical astronomy. IAU Colloquium 180, attended by 96 participants, was organized with 32 in-vited speakers and 44 poster papers. Sessions were devoted to Celestial Referenc