Many commercial processes take place through chemical reaction pathways, and a good grasp of reactor kinetics and reaction mechanisms will enable good design of processing equipment and parameters. This chapter covers a myriad of reactor engineering concepts, including both batch and continuous reaction systems (CSTR, PFR, packed bed reactors), bioreactor and microbial growth models, as well as homogenous and heterogeneous catalysis. Key concepts in reactor kinetics including rate laws, reaction mechanisms, residence time distributions, and biological growth patterns (e.g., Monod and Michaelis-Menten kinetics) can be effectively mastered from the practice problems presented in this book which mimic real-life problems. The inclusion of numerous visuals such as graphs and diagrams will also facilitate understanding of mathematical models and any abstract concepts. This chapter is not only relevant to the engineering field, but also applies to other disciplines from biology, chemistry, to geology and even cosmology.