The global adoption of all-solid-state lithium-ion batteries (ASSLBs) technology calls for high-performance solid-state electrolyte (SSE) components and the design of suitable processing strategies required for their integration into practical solid-state cells. Although they face their own unique set of challenges, oxide-based SSEs chemistry holds much promise for the practical demonstration of the next-generation ASSLBs. In this review, we systematically discuss the influence of oxide SSE additives on the electrochemical performance of ASSLBs using high-voltage cathodes and lithium metal anodes. We provide a broad spectrum of research activities on the use of additives to tackle some limited performance aspects surrounding oxide-based SSE single components. We showcase that, using additives, the microstructural and grain boundary engineering tools can provide considerable headroom for improvement of oxide-based SSEs performance in terms of ionic conductivity, mechanical properties and critical current density (CCD). Finally, we demonstrate the impact of additives on the interfacial behavior of oxide SSEs, including their use to design lithiophilic interfaces for Li anodes as well as their efficient role on the optimization of co-sintered all-oxide composite cathodes. To the best of our knowledge, this is the first review paper that covers the influence of oxide SSE additives on ASSLBs performance despite the immense body of literature work published in this area.