The advantages of solid electrolytes for new generations of high performance batteries are generally recognized. But these materials alone have no practical importance. Only suitable combinations of materials with well selected kinetic and thermodynamic properties are relevant and quite different features of solid state compared to liquid phase electrochemistry have to be taken into account. These requirements and an insight into the fundamental processes of cell operation will be discussed in terms of the various electrical and thermodynamic potentials. Electrons are often neglected, but play a most important role in the performance for both solid electrolytes and electrodes. Further, solid state electrochemical techniques will be discussed for enhancing and optimizing the search for suitable materials combinations for practical applications.