Under the banner of the current CERN EP R&D programme on technologies for future experiments, ESE is participating in the research and development of monolithic CMOS sensors. The aims are the development of CMOS sensors optimised for performance at the innermost radii and other flavours for use in the outer-layers. This includes cutting-edge research into, for example, the use of stitching and thinning to allow for truly cylindrical sensor shapes of wafer size with very low mass.