Sterilization is a process or killing all microorganisms (including spores) on or in a material or object. The factors that determine the type of sterilization or disinfecting process to be used include time, temperature, stage of growth of the organism, nature of the medium in which the organism is suspended (air, gas, liquid) and the number of organism present. Sterilization and disinfection can be achieved by using heat, filtration, chemical or radiation etc. Overall, heat is the best means of sterilization, but other methods are used for heat labile objects. Dry heat requires more time than wet heat to kill organisms, boiling kills most vegetative cells but not bacterial spores & pressure cookers &autoclaves achieve sterilization.