We describe the results of systematic measurements, carried out with single and double GEM detectors with printed circuit read-out and having an active area of 10×10 cm 2, both in the laboratory and in a high-energy charged particles beam at CERN. Using fast analog readout electronics, we demonstrate efficiencies for minimum ionizing particles close to 100%, with typical signal/noise ratios above 50 and up to 10 3 for the single and double GEM configuration, respectively, and a time resolution of 15 ns fwhm. Localization accuracies around 40 μm r.m.s. have been obtained for perpendicular tracks, degrading to 200 μm at 20° of incidence to the normal. Operated in a non-flammable gas mixture (argon-carbon dioxide), GEM detectors are robust, light and cheap to manufacture, and offer excellent performances and reliability suited for use in the harsh environments met at high luminosity colliders.