Solid-state batteries represent an exciting future direction for energy storage. While tremendous progress has been made in developing novel solids with very high Li-ion conductivity, electrochemical decomposition and reactivity of conductors with the anode or cathode material remains a major concern for the long-term stability of solid-state batteries. Using ab-initio computations we have evaluated the chemical and electrochemical stability of a large number of coating materials and conductors. I will discuss the clear set of chemical rules that appears from these results. Interestingly, the optimal coating materials depend very much on the specific electrode/conductor interface that needs to be protected.