This chapter presents the fundamental concepts and definitions of chemical kinetics theory applied to combustion science. Chemical kinetics allows for the introduction of time as an independent variable, therefore extending the understanding of combustion processes. The chapter discusses the elementary reactions, as well as their types, in the context of combustion. The law of mass action and the Arrhenius law are introduced to study the time evolution of species concentration in elementary reactions. The specific reaction rate constant is defined through the Arrhenius law, and the specific reaction rate constant of the reverse reaction is obtained by applying chemical equilibrium considerations. The chapter also discusses chemical kinetic mechanisms with emphasis on hydrogen, hydrocarbons, methanol, and ethanol. It is emphasized that detailed mechanisms are postulated, which means that they need to be validated with data from fundamental experiments. Finally, methods for reducing chemical kinetic mechanisms and general aspects of one-step kinetic mechanisms are also presented.