Understanding microbial inactivation kinetics is important in determining the efficacy of various biocides and the rate and extent of inactivation under different exposure conditions. Microbial inactivation is a kinetic process wherein the viability of organisms exposed to an inactivation agent varies as a function of time. Inactivation kinetics depends on the type of organism, type and concentration of biocide and for some disinfectants, environmental conditions such as temperature and pH. Complexities of cell physiology and differences in inactivation mechanisms make the analysis and interpretation of inactivation kinetics even more complex. If the inactivation data are generated experimentally for a limited set of environmental conditions, mathematic or statistical approaches can be used to develop formulas to predict the inactivation data for a process that includes the given conditions. Such kinetic-based models can play an important role in predicting the extent of inactivation of microorganisms under a variety of environmental conditions during processes of disinfection or sterilization. Previously established kinetic-based approaches for disinfection or sterilization processes that can be adapted to treat infections wastes and equipment are described in this. Some mechanistic and empiric disinfection models are also dealt with. Also discussed are the effects of environmental factors on the rate and extent of inactivation.