Abstract. The Micromegas technology can be used to construct very powerful detectors for low background, low energy measurements. A Micromegas X-ray detector has been used to search for solar axions in the CAST experiment at CERN. The detector has an active area of 7 cm × 7 cm, a very good x-y position, and a good energy resolution. It is built using low radioactivity materials and it is capable of low energy X-ray measurements of a few hundred eV. Despite the lack of external shielding the obtained background level is below 5 × 10⁵ counts/keV/cm²/s. The detector is being upgraded with a reduced active area Micromegas module, a focusing X-Ray telescope and shielding, which are expected to further reduce the background by about two orders of magnitude.