The pyrolysis process consists of the thermal degradation of biomass feedstock, in the absence of oxygen/air, leading to the formation of solid (charcoal), liquid (tar and other organics) and gaseous products (methane, ethane, carbon monoxide, etc). Pyrolysis can be used as an independent process for the production of useful energy (fuels) and/or chemicals. It also occurs as the first step in gasification or combustion process. An understanding of the chemical processes and transport mechanisms of biomass pyrolysis is important for many applications including optimization of boilers and large scale furnaces, estimating the dominant design variable in pyrolysis reactor and gasifier. This book focuses on modeling and simulation studies of pyrolysis of biomass particles. Dominant design variables are identified for pyrolysis process through sensitivity analysis. The models on pyrolysis of biomass are corrected, updated, and also new models are proposed by incorporating the shrinkage effect. The results are very useful for the design of pyrolysis reactor and gasifier. This book is suitable for students in all engineering discipline. It will also be helpful to research scientist.