An experimental and modeling study of reburning with biomass is presented. The experiments are conducted in an entrained flow reactor and in a pilot scale facility. The effects of reburn fuel (biomass char, wheat straw, and poplar wood) and process conditions (i.e., stoichiometry, temperature, particle size) are investigated. The model is a chemical reaction engineering type of model with a detailed reaction mechanism for the gas-phase chemistry, together with a simplified description of the mixing of flows, heating and devolatilization of particles, and gas-solid reactions. The different subsets and the complete model are validated against experimental results from the present work, as well as from the literature. The model provides a good description of reburning with both gaseous and solid fuels. However, further experimental work is needed for a more complete validation of the model.