Biomass is one of the important renewable energy sources. Biomass fuels exhibit a range of chemical and physical properties, particularly size and shape. Investigations of the behavior of a single biomass particle are fundamental to all practical applications, including both packed and fluidized-bed combustion, as well as suspended and pulverized fuel (pf) combustion. In this paper, both experimental and mathematical modeling approaches are employed to study the combustion characteristics of a single biomass particle ranging in size from 10 mu m to 20 mm. Different subprocesses such as moisture evaporation, devolatilization, tar cracking, gas-phase reactions, and char gasification are examined. The sensitivity to the variation in model parameters, especially the particle size and heating rates, is investigated. The results obtained from this study are useful in assessing different combustion systems using biomass as a fuel. It helps to clarify the situations where the thermally thin and thermally thick cases interface. It is clear that simple models of particle combustion assuming constant particle temperature are sometimes inadequate and that for large particles a more detailed mathematical representation should be applied.