While the importance of electrolyte chemical stability and ionic conductivity has been known since the very first batteries, findings in the lithium-oxygen battery community over the past few years have revealed that the electrolyte can dramatically alter the reaction pathway, battery capacity and rate. In this talk, the various mechanisms through which electrolyte has been found to interact with lithium-oxygen battery chemistry are explored. This includes recent results on the influence of solvent, counter anion and lithium ion concentration on the thermodynamics and kinetics of oxygen reduction as well as solvent-water-halide interactions and their impact on the viability of lithium halide redox mediators. Based on these new understandings, a framework for rational electrolyte design in lithium-oxygen batteries for controlling the reaction pathway and properties is discussed. This framework is based on competing interactions between solvent, co‑solvent/additives as well as charged species in the electrolyte and how these interactions can be altered by changing the nature and concentration of species present in the electrolyte. Opportunities and perspectives for unlocking this approach in other reactions will also be considered.