We have designed and built the echelle spectro- graph FOCES fed by 100 m optical bres to be mounted at the Cassegrain focus of either the 2.2 m or the 3.5 m telescope at the Calar Alto Observatory. The spectro- graph itself follows a white-pupil design collimated with two o-axis parabolic mirrors. The 15 cm beam leaving the 31.6 lines/mm R2 echelle is refocussed in the vicin- ity of a small folding mirror which allows ecient removal of scattered light. The cross-dispersion is achieved with a tandem prism mounting, and the beam imaged with an f=3 transmission camera onto a eld centered on a 1024 2 thinned Tektronix CCD with 24 m pixel diameter. The echelle image covers the visible spectral region from 380 to 750 nm displayed in 70 spectral orders with full spectral coverage. Spectral orders are separated by 20 pixels in the blue and by 10 pixels in the red. The maximum spectral resolution is R = = = 40600 with a 2 pixel reso- lution element; unvignetted resolution as dened by the bre alone would be obtained at R = 18000. Replacing the CCD by a 2048 2 chip with 15 m pixel diameter and taking into account light losses from a reduced entrance slit width a full 2 pixel resolution ofR = 65000 is obtained. The above concept has made FOCES an extremely well-dened instrument. A number of successful test in- stallations at the Cassegrain foci of the Wendelstein 80 cm telescope, the Calar Alto 2.2 m and 3.5 m tele- scopes has produced spectra of high quality for up to 60 min exposures. The limiting magnitude for a1h r ex- posure with an S=N ratio of 100 scales to V =1 2 for a 3.5 m telescope which is only slightly less than expected from laboratory tests. In an alternative mode FOCES of- fers a second bre carrying the sky background signal to correct extremely faint object spectra. This mode obtains the required higher cross-dispersion from an additional grism resulting in a correspondingly reduced spectral cov- erage.