In this paper we consider fuzzy control system as nonlinear control systems. We present an unifying framework of methodologies and summarize three different methods. The first one is based on the geometrical interpretation of the system dynamic behaviour in the phase portrait. The second uses stability and robustness indices defined from the qualitative theory of dynamic systems. The third method adopts the input-output stability approach by using the conicity criterion. These methods provide the basis for the development of new methodologies for the design of stable and robust fuzzy control systems.