Due to the intermediate operating temperatures (400-600oC), protonic ceramic electrochemical cells have attracted significant attention in the last 10 years because of the demonstration of potential applications of fuel-flexible fuel cells, water electrolysis to produce hydrogen, solid-state ammonia synthesis, electrochemical reduction of carbon dioxide to fuels, and fuel processing (e.g., natural gas to liquids). In addition to developing specific fuel electrodes for different electrocatalytic reactions, we need to discover new electrolyte and oxygen electrode materials generically for all the protonic ceramic electrochemical cells to further decrease the operating temperatures, increase performance, and prolong the long-term stability. The recently emerging materials of high entropy perovskite oxides have been reported to be able to serve as promising electrolyte and oxygen electrode materials. In this talk, we will summarize what Clemson University has done about developing, characterizing, understanding, and demonstrating high entropy perovskite oxides as high-performance and stable electrolyte and oxygen electrode materials for protonic ceramic electrochemical cells.