At five sites, laser-interferometric detectors, with armlengths ranging from 0.3 to 4 km, are being built. By using advanced optical technologies early on, the German-British project GEO 600, although only intermediate in size (600 m), has good chances for a competitive sensitivity. Particularly the use of the so-called signal recycling technique will allow a search for faint sources of only slowly varying frequency (pulsars, close binaries). First science runs of GEO 600 are expected in the year 2001.