Catalytic upgradation of lignocellulosic biomass to produce value-added fuels and chemicals is technologically challenged due to the complexity of the biomass-derived substrates as well as the reaction media. In order to develop a potential biorefinery, fundamental understanding of the interaction of biomass-derived platform molecules with the catalyst surface and solvent and their behavior during a conversion process needs to be developed. In this regard, computational chemistry methods such as ab initio density functional theory (DFT), classical molecular dynamics (MD), ab initio molecular dynamics (AIMD), Car-Parrinello molecular dynamics (CPMD), etc. have made a valuable contribution. This chapter briefly describes the role of these methods in understanding the reaction mechanism on the catalyst surface and the role of solvents in biomass conversion processes and pyrolysis chemistry. © Springer Nature Switzerland AG 2021. All rights reserved.