From the standpoint of waste elimination and the design and operation of the systems installed, the cogeneration of electricity and heat from the incineration of wastes has become today an important issue in Switzerland. Decision models developed to minimize the total costs associated with such systems respond only partially to the problems associated with the choice of configuration (synthesis), component design, and the operation of the waste incineration/cogeneration unit. In fact, the time factor which greatly affects certain key parameters such as the amount of wastes and the electrical and heating demands placed on the system (to name just two) renders the problem of synthesis, design and operation very complex. The thermoeconomic methodology presented in this article is a general approach which can be used to respond to the questions: when to invest and reinvest and which technology, configuration, component capacity and performance and modes of operation to adopt. The problem consists of developing the thermoeconomic models (typically very non-linear, continuous and/or non- contiguous) which can be used to minimize the time integral of total costs, optimizing simulateously the configuration, design and operation of the installation over its entire economic lifetime.