Combined cycle power plants burning natural gas offer various advantages such as high efficiency, low environmental impact, smaller specific investments and shorter construction periods which lead to a more flexible response to uncertain future electricity demands. The synthesis (choice of configuration), the design (capacities and performance of components) and the operation (changes in thermodynamic parameters) have to respect thermodynamic, economic and environmental factors. Thermoeconomic and environomic modeling and optimization provide powerful tools to simulaneously take these factors into account (see chapters 1 and 2 of this report). In contrast to the traditional approach of selecting the best among a limited number of proposed solutions, the unified modeling provided by thermoeconomic and environomic approaches makes it possible to find the region which may contain a number of plausible “optimum” of all possible solutions when combined with optimization algorithms from operation research. Sensitivity sudies of certain parameters on this optimum can then easily be made. A thermoeconomic model of a combined cycle plant and its connection to an existing gas pipeline was developed and compared with industry-designed plants (see chapters 3 to 5). An exergy analysis was also done on this combined cycle (see chapter 6). The use of thermodynamic and thermoeconomic optimization is demonstrated by an efficiency optimization and a sensitivity study of the effect of fuel price variation on the optimum plant synthesis and design (see chapter 7). Further. innovative technological options for combined cycle plants are presented in chapter 8. Chapter 9 introduces an environomic methodology and provides some background information with respect to environmental economics.