Despite early acceptance of In-Situ Combustion by the industry, current reality indicates a decline in its selection and implementation as a preferred option for heavy oil recovery. This decline can be attributed to the notion that In-Situ Combustion is unreliable mainly due the failure of some high profile pilot and indeed commercial application of In-Situ Combustion. However a more pertinent reason for its decline is the generally low technical understanding of the principles, processes and practice of In-Situ Combustion. The objective of this monograph is to present a literature review of the principles, process and practice of In-Situ Combustion and to evaluate its suitability as a viable alternative to steam injection in reservoirs where the conditions are not optimum for the implementation of Steam injection.