The fourth HST Calibration Workshop was held October 17-18, 2002 at the Space Telescope Science Institute. The workshop featured reports from the commissioning of Advanced Camera for Surveys (ACS) and the re-commissioning of NICMOS. New calibrations and advances in the understanding of STIS, WFPC2, FOS, and the FGS were also presented, as well as previews of calibration plans for COS and WFC3 which are scheduled to be launched in approximately two years. The workshop was designed to foster the sharing of information and techniques between observers, instrument developers, and instrument support teams. Approximately 120 astronomers attended the workshop which included 32 talks, 40 posters, and time for demos and splinter groups on various topics.