In 2019, the CO2M mission has been selected by the ESA as Sentinel 7 in Copernicus programme, which will be measuring CO2 concentration in terms of column-averaged mole fraction (denoted as XCO2). The payload comprises a suite of instruments addressing the various aspects of the challenging observation requirements. A push-broom imaging spectrometer will perform co-located measurements of top-of-atmosphere radiances in the near infrared (NIR) and short-wave infrared (SWIR) at high to moderate spectral resolution. A multi-angle polarimeter is co-located measurements of aerosols performed. Finally, measurements of a three-band cloud imager, co-registered with the CO2 observations, will provide the required cloud-flagging capacity at sub-sample level. This paper will review the results of the Phase A/B1 instrument studies, including technology pre-development activities, preliminary design of the CO2M mission′s instruments, etc.