The XMM Project Scientist will issue calls for proposals in ``Announcements of Opportunity'' (AOs) in regular intervals. The first AO, AO-1, is for open time during the first 27 months of the mission. 70% of all open time will be scheduled at first, based on a preliminary (and conservative) estimate of the observatory's efficiency. A supplementary call for proposals for the remaining 30% of open time will be issued later. Subsequent AOs will be for periods of one year (TBC).
Policies concerning, e.g., duplication avoidance, proposal categories (GO, ToO) or target categories (stars, galaxies, AGNs etc.) are described in the AO-1 documentation and the XRPS Users' Manual.