Super-ionic conducting oxide (SCO) electrolytes are a unique subset of ceramic electrolytes that offer numerous benefits in the development of solid-state battery technology. First, SCOs are typically synthesize in air and are reasonably stable in ambient air. This stability can simplify cell fabrication, reduce packaging mass, and dramatically improve safety. Second, the thermal stability and increasing conductivity with an increasing temperature can enable an inherently stable cell chemistry that reduces peripheral component such as thermal management and power electronics. In the context of electric vehicles, this can significantly reduce the battery pack mass, cost, and complexity. Third, consisting of stable inorganic materials, solid state oxide batteries can considerably have a longer cycle life compared to liquid electrolyte technology. Indeed the features offered by solid-state batteries are appealing; however, there are few examples of bulk-scale SCO-enabled technology. Interestingly, it is not due to the lack of available state-of-the-art SCOs, rather it is the numerous processing, scaling and integration challenges that have limited the advancement of bulk-scale solid-state battery technology. For example, most oxide ceramics require high temperature processing to bond or sinter components together. How the high temperature processing affects reactions with electrodes is a considerable issue. Similarly, maintaining adequate electrolyte/electrode contact area without amplifying chemical reactions is challenging and requires novel cell stack designs and fabrication techniques. In bonding and operating monolithic batteries, mechanical properties are of particular importance since most ceramics are relatively brittle. Lastly, and perhaps most importantly, identifying SCOs with inherent stability against Li or developing technology to enable the use of state-of-the-art SCOs is the key. —J. Sakamoto in Handbook of Solid State Batteries