A summary of an ESA/ESTEC sponsored technology research programme is given aiming at the development of a CO2 partial pressure sensor suitable for monitoring the PP CO2 inside the oxygen ventilation loop of the EVA life support module.At first, a trade-off of candidate sensor concepts is presented. As result, the infrared optical sensor concept has been selected. In the frame of a discussion on basic facts of IR absorption the rationale for the selected configuration of the IR sensor is given. A breadboard model of the PP CO2 sensor together with a test set-up has been established. The sensor was subjected to a test programme consisting of two separate test periods. The main results are given. Finally, the findings are discussed in the light of the development of future flight hardware.