Laser-based in situ diagnostic techniques with high temporal, spectral, and spatial resoln. have become valuable tools to study the mol. dynamics of gas-phase and heterogeneous reactions as well as complex tech. combustion processes. Results of recent expts. are presented in which laser-induced fluorescence, sum-frequency generation surface vibrational spectroscopy, Rayleigh scattering, excimer laser-induced fragmentation fluorescence, and high-resoln. tunable diode laser absorption spectroscopy were applied to investigate elementary chem. gas-phase and catalytic combustion reactions, internal combustion engine processes, as well as coal combustion and waste incineration.