This book presents a thermodynamic and economic analysis of gas-gas systems in power plants, including combined heat and power systems, combined cooling, heat and power systems, hydrogen production facilities and compressed energy storage system. A configuration for high-temperature gas-cooled nuclear reactor is also used as a heat source for the cycle. The book compares different technologies, such as gas-steam and gas-gas systems, using optimized cases. It presents mathematical models that return optimal thermodynamic parameters of the cycles, and applies a novel continuous-time model in order to perform an economic analysis as well. This book utilizes numerous illustrations and worked examples to thoroughly explain the technologies discussed, making it relevant for researchers, market analysts, decision makers, power engineers and students alike. .