In this chapter, the study of kinetics is introduced by examining homogeneous reactions. The relationship between kinetic law and reaction mechanism is stressed introducing the concepts of elementary steps, slow-rate-determining steps, and steady-state conditions. The rate law is derived from a reasonable hypothesis of a reaction mechanism and is introduced in the mass balance equation that differs according to the employed reactor, that is, well-stirred batch, semi-batch, continuous reactor, or alternatively, tubular-packed bed reactor. The characterization methods for determining the ideal behavior of these different types of reactors are described. The schemes of multiple reactions (equilibrium, competitive, and consecutive reactions) are discussed and a general approach is given to the kinetic description of complex schemes. The kinetic approach to radical chain and enzymatic reactions is examined on a theoretical basis, enriched with different examples and exercises. Many other examples of kinetics are reported, with exercises and MATLAB code, associated with these exercises, available online.