The CIRM projects is dedicated to constraining the C isotopic reservoir on Mars from surface to space using a combination of measurements from different orbiters and facilities, together with the development of numerical models accounting for isotopic fractionation. Observations from NASA Infrared Telescope Facility will probe the ¹³C/¹²C isotopic ratio in the near-surface carbon dioxide atmosphere. Solar occultation observations from the ExoMars Trace Gas Orbiter will provide measurements ¹³C/¹²C in the CO₂ vertical structure from 10 to 120 km. Mass spectroscopic measurements from JAXA’s Martian Moons eXploration mission will measure in situ the C isotopic ions escaping through the induced magnetotail. The analysis of these measurements will be combined with the development of a unified photochemical and escape model from surface to space accounting for isotopic fractionation, aiming to better understand the physics of the escape of C from Mars throughout history.