The Science Program Committee of the European Space Agency approved participation to the XRISM (formerly known as XARM) mission at the meeting of July 2017. According to the terms of the Memorandum of Understanding between ESA and JAXA, ESA shall coordinate the provision of, and delivery to JAXA of the following hardware items:

• Loop heat pipes for the Resolve;
• Filter wheel mechanism and electronics including High-voltage power sources and Calibration sources (developed at the University of Geneva and SRON);
• Star Trackers;
• Magnetic Torquers;
• Geomagnetic Aspect Sensors.

The same agreement stipulates that the XRISM Science Team (ST) comprises seven European scientists (later augmented to eight). Two ST members were appointed as “Participating Scientists” through a competitive process led by ESA, while the others were appointed by the following ESA Member States because of their specific contribution to the Mission: Netherlands and Switzerland.

A small number of "XRISM Guest Scientists" (XGSs) have been selected based on a peer-reviewed competitive process prior to launch, and granted access to specific observations carried out during the XRISM Performance Verification phase.

In consideration of ESA’s contribution, not less than 8% of the total Guest Observing Time, or an equivalent return as mutually agreed, shall be allocated to ESA. This time will be allocated by ESA through a competitive process open to the scientific community of the European member states.