Solid-state batteries are currently considered as next-generation lithium-ion batteries, the goal being to replace flammable organic lithium conducting electrolytes with solid-state ionic conductors. A variety of material classes are being considered, but sulfide electrolytes have attracted substantial interest due to their high ionic conductivity and favorable mechanical properties. Here, the families of Li10(Ge/Sn)P2S12 and Li6(P/Sb)S5X (X = Cl, Br, I) are, so far, the only Li + compounds exceeding 10 mS cm -1 at room temperature. The structure and transport of these materials have been widely investigated, and the ionic conductivities have been pushed continually higher, reaching values reasonable for solid-state battery operation. While both are excellent ionic conductors, they have fundamentally different crystal structures. In Li10(Ge/Sn)P2S12, the diffusion of Li + is dominated by channels for fast Li + conduction. In the argyrodite family Li6(P/Sb)S5X, ionic transport is isotropic and strongly influenced by a crystallographic S 2-/X -disorder that affects the lithium distribution. Nevertheless, the fast-ionic transport and large structural differences make these materials ideal for investigating fundamental questions in solid ionic conductors. In particular, they provide the opportunity to identify trends that are independent of the crystallographic structure.