AbstractThe Röntgensatellite ROSAT has been in orbit since June 1,1990. After a 6‐month all‐sky survey ˜ 6,500 pointed observations have been performed. In total more than 150,000 X‐ray sources have been detected. Among the various object classes observed are comets, stars, white dwarfs, cataclysmic variables, neutron stars, black hole candidates, supernova remnants, nearby galaxies, AGN, and clusters of galaxies. Many of these objects are known to be time variable sources. Various catalogues of sources found in the ROSAT All‐Sky Survey and in the pointed observations are used as the basis for studying the temporal behaviour of ROSAT sources. This paper deals with the description, production and content of the various ROSAT catalogues with particular emphasis on the usefulness for the study of source va