In this chapter a methodology for the unsupervised design of microwave devices, circuits and systems is considered. More specifically, the application of the Particle Swarm Optimizer and its integration with electromagnetic simulators is discussed in the framework of the microwave circuits and devices design and optimization. The idea is to automatically modify the characteristics of the device in an unsupervised way, with the goal of improve the device performances. Such kind of CAD tool could be the solution to reduce the time to market and keep the commercial predominance, since they do not require expert microwave engineers and it can reduce the computational time typical of the standard design methodologies. To assess the potentialities of the proposed method a selected set of examples, concerning the design of microwave planar devices such as filters, splitters, and other microwave devices under various operative conditions and frequency bands, are reported and discussed. The chapter also includes a brief discussion concerning different strategies, such as parallel computation, to reduce the computational burden and the elaboration time. The obtained results seem to confirm the capabilities of the proposed method as effectiveness microwave CAD tool for the unsupervised design of microwave devices, circuits and systems. The chapter ends with some conclusions and considerations related to ideas for future works.