The fundamental laws of mass, heat, and momentum transport are briefly presented in this chapter and their relationships with chemical kinetics depicted. The approach presented starts with estimation of basic properties like viscosity, thermal conductivity, and mass diffusivity, all of which are of fundamental importance in describing transport phenomena. Transport phenomena originate gradients in temperature, pressure, and concentration that are the driving forces for transformations occurring in a system. Two scales of transformation can be considered, i.e., molecular and macroscopic. Molecular-transport phenomena are normally much slower than macroscopic ones, and this can result in a limitation on chemical reaction rates. In this chapter, detailed examples of basic property calculations are reported as are examples of chemical gas–solid reactions limited by diffusional resistance (like ammonia oxidation). Finally, a great part of the chapter is dedicated to the evaluation of catalyst effectiveness factor. MATLAB code associated with the examples in this chapter is available online.