The purpose of this SAE Aerospace Information Report (AIR) is to provide information that would be useful to potential users/operators and decision makers for evaluating and quantifying the benefits of an Engine Monitoring Systems (EMS) versus its cost of implementation. This document presents excerpts from reports developed to analyze actual aircraft cost/benefits results. These are presented as follows: a. first, to outline the benefits and cost elements pertaining to EMS that may be used in performing a cost versus benefits analysis; b. second, to present considerations for use in conducting the analysis; and c. third, to provide examples of analyses and results as they relate to the user/operator and decision-maker community. The document encompasses helicopters and fixed wing aircraft and distinguishes between civilian and military considerations. This document is not intended to be used as a technical guide, nor is it intended to provide methodologies, be a legal document, or be a standard. The findings are informational and are presented in the words of the report authors.