This short course will cover the fundamental principles of reciprocating compressors and engines. For the compressor, this will include discussions of PV diagrams, capacity, volumetric efficiency, and horsepower. In addition, it will cover the effects of changing conditions, gas analysis, temperature, and pulsation on compressors. For the engine, discussions of the sequence of events for two-stroke and four-stroke engines that include pressure and vibration patterns with respect to volume and time will be presented. Finally, it will briefly cover engine combustion characteristics for a few common cases.