This chapter discusses kinetic modelling of the gas-phase chemistry for biomass combustion under oxy-fuel conditions. Several datasets of species mole fraction measurements obtained from counterflow flames covering a broad range of conditions and fuels were utilised to assess the progress in detailed kinetic modelling of polycyclic aromatic hydrocarbons and to identify a detailed chemical kinetic model suitable for further investigations of solid fuel combustion under oxy-fuel conditions. The selected model was amended by a \(\text {NO}_x\)  submodel and the oxidation chemistry of oxygenated and nitrogen-containing tar species, i.e. anisole, levoglucosan, propionaldehyde, ammonia, and pyridine. A multistep reduction approach provided a skeletal kinetic model for biomass gas-phase combustion with 104 species (140 species, including the \(\text {NO}_x\)  submodel), which can be used to perform complex simulations at reduced computational cost. The validation of these skeletal models against experimental data representative of atmospheric high-temperature combustion under oxy-fuel conditions and in air demonstrated the models’ prediction accuracy and suitability for practically relevant applications.