The proceedings of a workshop held at the European Southern Observatory in September 1999, the 4th workshop of a series, which concentrates on optical detectors for astronomy. Representatives from every leading manufacturer and all major astronomical observatories came together to present their work on Charged Coupled Devices (CCDs). The papers presented in these proceedings are concerned with the development, manufacture, testing, implementation, new techniques and applications of CCDs. Many discuss the electronics that are used to operate these detectors. Astronomical observatories are the most ambitious and aggressive users of optical detectors, more so than any other scientific discipline. Since the quantum efficiency and noise of a detector have a direct effect on the quality of science, the makers of astronomical CCD systems continually "push the envelope" of optical detection technology. The papers contained in these proceedings provide the reader with the state of the art in CCD technology and contain information on research and development efforts, for ground-based and space-based applications, that should continue for several years.