The design of future combustion systems will require a thorough understanding of the combustion processes. This understanding can only be obtained through the characterization of experimental combustion media. Although there are various types of diagnostic techniques available for this characterization, optical techniques are more attractive because they often permit in situ measurement--with spatial and temporal resolution--of such parameters as gas temperature, species concentration, and flow velocity, without introducing any disturbance to the process being analyzed. Such optical techniques include laser Raman scattering, laser-induced fluorescence, coherent anti-Stokes Raman scattering, laser Doppler velocimetry, and absorption and emission spectroscopy. Of these, the first three techniques--laser Raman scattering, laser-induced fluorescence, and coherent anti-Stokes Raman scattering--will be examined in depth at this seminar. These three techniques, while somewhat different in principle, can all be used for the measurement of temperature and species concentration. Included in the discussion will be an overall tutorial review of the theoretical background, various experimental methods, and the capabilities and limitations of these techniques. Also discussed will be the relative merits of these techniques as they relate to combustion diagnostics. In addition, the requirements for the instrumentation and laser sources which are needed to fully utilize these methods will be addressed.