Optical and UV monitor (OM) on-board XMM-Newton

The Optical and UV Monitor (OM), is a small telescope co-aligned with the main XMM-Newton X-ray telescopes. It can perform imaging with six broad band lenticular filters covering the range 180 nm to 600 nm. In addition, two grisms allow the user to obtain low resolution spectra in the same range. The detector is an intensified CCD. The instrument is fully calibrated in the standard UBV Johnson system and also in absolute flux for both filters and grisms. We describe the instrument and its calibration. We present some results and usage statistics.