Many simple molecules, such as H2O, CO2, CO, N2O, CH4, and HCN, have strong absorption bands at wavelengths between 2 and 3.5 micrometers . We are developing InGaAsSb/AlGaAsSb multi-quantum-well diode lasers operating from 2 to 3.5 micrometers as sources for trace-gas monitors. These devices are grown by molecular beam epitaxy, and they generally comprise four or five InGaAsSb quantum wells separated by AlGaAsSb barriers. The cladding layers are high-Al-content AlGaAsSb layers. Our longest-wavelength, room- temperature (20 degree(s)C) lasers operate at 2.78 micrometers in the pulsed mode, delivering 95 mW peak power. The highest temperature for pulsed-mode operation is 60 degree(s)C, at which the wavelength is 2.9 micrometers . Between 78 and 200 K they operate cw, and at 200 K the output is 3 mW at 2.66 micrometers in a dominant single mode. We discuss the properties of these lasers along with some initial applications to water-vapor detection.