Scientific CCDs have applications in astronomy, astrophysics and particle physics. Although CCDs main application is as high quality photo-sensors, some of these silicon devices have enough thickness and mass and are excellent detectors for direct dark matter search and other particle and nuclear physics applications. A key benefit of these CCDs is their low noise which allow them to detect few eV of energy. For astronomy a low noise CCD system will benefit spectroscopy measurements. In order to use their full potential readout systems with noise performances around or below 1 electron are needed. This paper reports on the R&D that has led to readout systems with that level of performance.