The thesis describes the characterisation and application of the laser induced incandescence technique for making soot measurements in practical devices. Laser induced incandescence is the phenomenon whereby particulates such a soot absorb laser radiation and are heated to a temperature much higher than the bath gas. The broadband incandescence signal from the hot particles can be detected and the signal is proportional to volume fraction. The technique was used to study soot in partially premixed counterflow ethylene air flames, iso-octane explosion flames, and to image soot in a D. I. Diesel engine. Mie scattering, OH-LIF and absorption were used a complementary diagnostics. Appropriate ratios of LII and Mie images allowed the relative particle size and number density to be imaged. The counter flow burner measurements were used to study the effects of strain on soot formation while the bomb work demonstrated soot production in hydro-dynamically unstable cellular flames. The Diesel engine measurements are a demonstration of optical diagnostics in a real device. In order to characterise the LII signal behaviour two types of carbon aerosol generators were built. The liquid dispersion device produces almost spherical sub-micron carbon black particles. The device was used to characterise the soot field response, laser fluence response, signal decay and spectrum of the LII signal.