Tunable diode laser absorption spectroscopy (TDLAS) meets the major requirements for atmospheric trace gas monitoring, which are sub-ppbv sensitivity, high detection speed and the potential for simultaneous in-situ measurements of several compounds. In recent years, several multi-laser TDLAS systems have been developed at the Max Planck Institute for Chemistry and used in a number of ground based, shipboard and airborne field campaigns to measure the concentrations of atmospheric trace species, e.g. N2O, CH4, CO, HCHO, H2O2 and NO2, from the boundary layer up to the lower stratosphere at 14 km altitude. During these field measurement on various platforms, detailed comparisons of TDLAS with other techniques have been performed for CO, HCHO, and NO2, yielding an agreement between the various instruments on the order of 10-20 percent. In addition, a TDLAS instrument has been used to measure N2O fluxes from soils by eddy correlation and flux gradient techniques. A particular TDLAS instrument has been developed, which is capable of high-precision direct measurements of 13CH4/12CH4 and 12CH3D/12CH4 ratios. An intercomparison between this instrument and conventional mass spectrometry yielded a mean deviation of (delta) 13C equals 0.5 percent and (delta) D equals 5 percent.