Potassium-ion batteries (PIBs) are promising as a low-cost and complementary technology to lithium-ion batteries (LIBs) because of the relative abundance of potassium. Electrolyte is a critical component and governs the electrochemical performance of PIBs. Electrolyte engineering has recently resulted in promising results for both the anode and cathode materials of PIBs. However, the performance of current PIBs is still limited for practical applications. A systematic analysis of recent electrolyte engineering research is required for further improvement. In this review, we first summarize the recent electrolyte research progress and design strategies for PIBs. We then discuss the key features of PIB electrolytes such as the K-ion solvation environment and SEI chemistry, and finally propose several design strategies and considerations for future electrolyte development.