Publisher Summary This chapter discusses thermobacteriology as it is applied to food processing with a brief description of the methods of process evaluation, special attention being given to fundamental concepts on which development of the methods is based. The chapter indicates some of the many problems that still exist with regard to further refinement in the art of thermal processing of foods. A critical analysis of process evaluation methods has been presented, in which it was shown that mechanism of heat transfer within the food container during process are considered if greatest accuracy in process evaluation is to be attained. A method was suggested for ascertaining the location in the container where probability of bacterial survival is greatest. The General Method and Ball's mathematical methods of process evaluation are discussed based on the concept that a thermal process adequate to accomplish sterilization of the food at the point of greatest, temperature lag in a container during process is adequate to sterilize all the food in the container. The General Method has been improved to the extent that it is now quite applicable for calculation and evaluation of processes for foods exhibiting the more complex heating curves. A series of nomograms for the graphic calculation of thermal processes has been described for non-acid foods exhibiting straight-line, semi-logarithmic heating curves. Use of these nomograms greatly shortens the time required for calculations. The chapter discusses the concept regarding the effect of heat on bacteria in light of present knowledge concerning the order of death of bacteria when subjected to heat. Because of the practical implications involved, this subject has been treated in detail.