Magnesium is attractive as an anode owing to its high capacity and abundance in the Earth's crust. It remains a challenge to realize efficient plating and stripping in electrochemical cells with a Mg anode, due to its reactivity with conventional liquid electrolytes comprising fluorinated salts. We hypothesized that the reactivity of species in the electrolyte may be controlled through solvation structure in concentrated electrolytes as well as those featuring a fluorinated diluent, which aids in reducing the viscosity and maintaining high ionic conductivity. Here, I will describe our efforts to understand solvation structure and reactivity at Mg–electrolyte interfaces. In turn, I will highlight how specific compositions are impactful in sustaining the electroreversibility of Mg anodes for hundreds of hours of continuous operation with low overpotential. I will tie this behavior to the structure of the interphase, whose composition is divergent from what is typically observed for dilute and concentrated electrolytes. There are emerging implications stemming from our work that motivates the future design of artificial interphases for Mg anodes obviating the use of chlorides, which would otherwise corrode other components of the cell.