The review presents an overview of the recent advances in inorganic solid lithium ion conductors, which are of great interest as solid electrolytes in all-solid-state lithium batteries. It is focused on two major categories: crystalline electrolytes and glass-based electrolytes. Important systems such as thio-LISICON Li 10 SnP 2 S 12 , garnet Li 7 La 3 Zr 2 O 12 , perovskite Li 3x La (2/3) x TiO 3 , NASICON Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , and glass-ceramic xLi 2 S·(1 − x )P − 2 S 5 and their progress are described in great detail. Meanwhile, the review discusses different ongoing strategies on enhancing conductivity, optimizing electrolyte/electrode interface, and improving cell performance.