The Journées 2004 "Systèmes de référence spatio-temporels", with the sub-title "Fundamental Astronomy: New concepts and models for high accuracy observations", will be held from 20 to 22 September 2004 at Observatoire de Paris.

These Journées will be the sixteenth conferences in this series which have been organized in Paris each year from 1988 to 1992 and alternately, since 1994, in Paris and other European cities: Warsaw 1995, Paris 1996, Prague 1997, Paris 1998, Dresden 1999 ("also Lohrmann Colloquium)", Paris 2000, Bruxelles 2001, Bucharest 2002, St Petersburg 2003 (including an "Orlov session" as in 1998).

The purpose of this series of conferences is to discuss problems ranging from the concepts and realizations of space and time reference systems to the scientific interpretations of precise observations referred to these systems.

The problems to be discussed in 2004 are related to the International Celestial Reference System (ICRS), including new concepts in fundamental astronomy, the associated nomenclature (see for more details, "the IAU WG NFA webpage)" and the astronomical models for Earth rotation (precession, nutation, atmospheric and oceanic effects, etc.) at the highest level of accuracy consistent with the current and future precision and temporal resolution of the observations of Earth rotation.

The programme of the Journées 2004 will include five sessions, each one of approximately half-day duration.