After 36 years of operation, reactor Thetis at the Institute for Nuclear Sciences (Ghent University) was decommissioned in
December 2003. On this occasion, a survey is presented of the characteristics and features of Thetis, which were opening the
way to its significant contribution to NAA and its leading role in the development of the k0-standardization. A summary is given, including a few specific examples, of fundamental analytical developments and practical
applications based on irradiations in the reactor Thetis.