EFOSC is a standard ESO instrument operating at the Cassegrain focus of the 3.6 m telescope since April 1st, 1985. A description of its optical design and operating modes is given in Enard and Delabre (1982) and Dekker and D'Odorico (1985). Briefly, it is a focal reducer with spectroscopic capability. The collimator produces a collimated beam with a diameter of 40 mm which passes through a filter and/or grism. The f/2.5 camera focusses the beam on the detector which is at present a thinned, back-illuminated RCA CCD with 320×512 pixels. The pixel size is 30 μm which corresponds to .675″ on the sky. There are three remotely controlled wheels in the instrument: the aperture wheel in the focal plane of the telescope, with long slits of different widths, a filter and a grism wheel with 12 positions each. The instrument can be operated in four different modes: direct imaging, slit spectroscopy, grism or multiple object spectroscopy with specially made aperture plates.