Alexeï Molin, François Pajot, Marc Audard, Marco Barbera, Sophie Beaumont, Edoardo Cucchetti, Matteo D'Andrea, Christophe Daniel, Roland den Hartog, Megan E. Eckart, Philippe Ferrando, Luciano Gottardi, Maurice Leutenegger, Simone Lotti, Lorenzo Natalucci, Philippe Peille, Jelle de Plaa, Etienne Pointecouteau, Scott Porter, Kosuke Sato, Joern Wilms, Vincent Albouys, Didier Barret, Massimo Cappi, Jan-Willem den Herder, Luigi Piro, Aurora Simionescu

The X-ray Integral Field Unit is the X-ray imaging spectrometer on-board one of ESA's next large missions, Athena. Athena is set to investigate the theme of the Hot and Energetic Universe, with a launch planned in the late-2030s. Based on a high sensitivity Transition Edge Sensor (TES) detector array operated at very low temperature (50 mK), X-IFU will provide spatially resolved high resolution spectroscopy of the X-ray sky in the 0.2-12 keV energy band, with an energy resolution goal of 4 eV up to 7 keV [3 eV design goal]. This paper presents the current calibration plan of the X-IFU. It provides the requirements applicable to the X-IFU calibration, describes the overall calibration strategy, and details the procedure and sources needed for the ground calibration of each parameter or characteristics of the X-IFU.