Scientists and engineers in the 21st century have a great responsibility to solve environmental and energy problems for achieving a sustainable society. Our laboratory contributes to solve above-mentioned problems throughout fundamental and application researches on environmentalfriendly energy-conversion devices, such as fuel cells and rechargeable batteries. In particular, focusing on solidstate ion-conducting materials, we are challenging to establish an academic discipline on “solid-state ionics”, and applying this to develop novel materials and to improve performance/reliability of the energy conversion devices. We are also working for the development of advanced operando analytical techniques for solid-state ionic devices.