Combined cycle power plants are currently one of the most important options for the construction of new generating capacity as well as for the replacement and repowering of existing units. Due to the complexity and the large number of options and parameters available to such plants, finding optimized solutions for system synthesis, design and operation is very difficult if not impossible with these traditional methods such us case and parametric trade-off studies. This is especially true when advanced options as well as thermodynamic, economic and environmental criteria are considered. A thermoeconomic / environomic methodology to deal with these difficulties is presented here. Results for the application of this methodology to a 50 MW cogeneration combined cycle power plant are presented and discussed.