Lithium super-ionic conductor (SIC) materials are the key component in enabling all solid-state Li-ion batteries. However, it has not yet been understood why only a few materials as super-ionic conductors can achieve exceptionally higher ionic conductivity than typical solids and how one can design fast ion conductors following simple principles. Using ab initio modeling, we show that fast diffusion in super-ionic conductors happens through unique concerted migration mechanism of multiple ions with low energy barrier in contrast to typical solids. We elucidate that low energy barriers of the concerted ionic diffusion are a result of unique mobile ion configurations and strong mobile ion interactions in super-ionic conductor materials, such as Li₁₀GeP₂S₁₂, lithium garnet, NASICON, etc. Our theory provides a conceptually simple framework for guiding the design of super-ionic conductor materials. We demonstrate this strategy by designing a number of novel fast ion conducting materials to activate concerted migration with reduced diffusion barrier. The novel materials are predicted to have comparable Li⁺ ionic conductivity at room temperature to the known Li SIC materials. In summary, our proposed theory and identified mechanism are universally for fast diffusion in a broad range of ionic conducting materials, and provide a general framework and a universal strategy to design solid materials with fast ionic diffusion.