The basic SIR (susceptible-infectious-removed) model of epidemiology is presented in chemical kinetic terms with a simple two-reaction mechanism. The conditions for the development of epidemics, the course of a simple closed epidemic, and the bases of several mitigation strategies are described in terms of the underlying first- and second-order rate coefficients. Connections are made with the terminology used in epidemiology and in recent news reports on the COVID-19 pandemic.