The ROSAT project was an initiative from the Max Planck Institute for Extraterrestrial Physics (Max-Planck-Institut für extraterrestrische Physik; MPE) in Garching in 1975. Researchers from Germany, the United States and the United Kingdom were involved in the mission.

The tasks were distributed amongst the partners as follows:

• MPE was the scientific project leader (Principal Investigator: Joachim Trümper) and contributed two models of the Position Sensitive Proportional Counter (PSPC), a newly developed X-ray detector.
• After various studies and technical pre-development, the project was approved by the German Federal Ministry of Research and Technology (Bundesministerium für Forschung und Technologie; BMFT) in 1982. The German Aerospace Research and Development Centre (Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt; DFVLR) in Cologne, now the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), was responsible for managing the project.
• An industry consortium under the leadership of Dornier (now EADS Astrium) started building the satellite in Friedrichshafen in 1983. Carl Zeiss, based in Oberkochen, developed the telescope optics.
• The US space agency, NASA, was responsible for provision of the Delta II rocket and the launch.
• NASA also provided a second X-ray detector. The High Resolution Imager (HRI) was developed by the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
• In addition to the X-ray telescope, the satellite also carried a wide-field camera (WFC) to capture images in the extreme ultraviolet regime of the spectrum. It was provided by a British group under the leadership of the University of Leicester.
• The German Space Operations Center (GSOC) at DLR Oberpfaffenhofen was responsible for operating the satellite after its launch on 1 June 1990. From there, the data was forwarded on to the various data centres:MPE and NASA's Goddard Space Flight Centre for the X-ray telescope and the universities of Leicester and Tübingen for the WFC data.
• The Astrophysical Institute of Potsdam was involved in archiving and cataloguing the data in the 1990s.
• After the first mission phase – the all-sky survey – was completed, ROSAT was made available for a global guest observer programme. A total of around 4000 scientists from 26 countries took part in this programme.