Reactor kinetics has the purpose to analyze the time-dependent behavior of the neutron population in a nuclear reactor in response to operational transients, abnormal conditions and accidents. This chapter presents the one group point kinetics theory. Despite the development of Multi-energy-group multi-region kinetics calculations, the topic of point kinetics is still relevant from a didactic point of view. What’s more, point kinetics is still used in quasi static methods, and inverse point kinetics is the basis of reactivity meters and is used in the treatment of Dynamic Rod Weight MeasurementDynamic Rod Weight Measurement (DRWM) tests. This chapter presents the merging of delayed neutron percursors into either 6 or 8 groups, and emphasises the assumptions that allow the kinetic equations to be written.