This SAE Aerospace Information Report (AIR) discusses physical and functional integration of main engine and auxiliary power unit (APU) monitoring with other on-board systems. It includes General Considerations, Parameter Selection and Requirements, Signal Sources, Signal Conditioning, Data Processing, Data Storage, and Data Retrieval. Engine monitoring hardware and software are discussed so that they may be properly considered in an integrated design. Civil and military aviation applications are included and delineated where requirements differ.