The optimization of chemical processes has attracted attention because, in the face of growing competition, it is a natural choice for reducing production costs, improving product quality, and meeting safety requirements and environmental regulations. From an industrial perspective, the main objective is often economic and is stated in terms such as return, profitability or payback time of an investment.In this book, modeling, simulation and optimization of fluid catalytic cracking unit, (FCCU)was carried out. The heterogeneous catalytic cracking reactor was modeled as plug flow reactor (PFR) with the gas oil being the fluid mixed with the Magnesiev-370 catalyst, while the coke combustion reactor was modeled as continuous stirred tank reactor (CSTR). The model however was lumped as gas oil, fuel gas, gasoline, and bottom oil, thus the model was built in HSYSY simulation environment.The book focuses on providing processing engineering, modeling supports and optimization using a computer based simulator 'HYSYS' to help numerous refiners around the globe and researchers to develop a process optimization strategy for the FCCU