<p>The accelerating global demand for rechargeable energy storage and the raw-material constraints associated with lithium-ion batteries have catalysed the search for alternative battery chemistries. Among them, rechargeable magnesium batteries (RMBs) have emerged as a candidate owing to their high volumetric capacity (3,833 mAh cm⁻³) and the natural abundance and safety benefits of magnesium. However, the development of RMBs remains hindered by the lack of viable electrolytes, as magnesium analogues of conventional lithium-ion battery electrolyte formulations fail to support reversible magnesium deposition. In this Review, we examine the evolution of RMB electrolytes, from early Grignard-based complexes to emerging single-salt electrolytes, and discuss the fundamental design principles that have driven breakthroughs in electrolyte performance, stability and compatibility. Electrolyte chemistry dictates interfacial behaviour and dendrite formation, yet key knowledge gaps in understanding electrode–electrolyte interphases and magnesium-plating mechanisms continue to limit battery performance. Addressing supply-chain vulnerabilities will improve RMB production reliability, whereas minimizing hazardous electrolyte components strengthens its viability as a next-generation clean-energy-storage technology. By articulating a clear roadmap grounded in both mechanistic understanding and materials innovation, future electrolyte development can be guided towards the commercialization of RMBs.</p>