The kinetics of a detailed chemically reacting system can potentially be very complex. Although the chemist may be interested in only a few species, the reaction model almost always involves a much larger number of species. Some of these species are referred to as radicals. These are highly reactive species (usually of low concentration) which can be important intermediaries in the reaction scheme. A large number of elementary reactions can occur amoung the species; some of these reactions are fast and some are slow. The aim of simplified kinetics modeling is to derive the simplest reaction system which retains the essential features of the full system. In this lecture we describe an optimization-based method for reduction of the number of species and reactions in chemical kinetics models. Numerical results for several reaction mechanisms are given which illustrate the potential of this approach.