High-entropy materials (HEMs) tend to be composed of five or more elements or have a configurational entropy greater than 1.5R (R is gas constant). The high configurational entropy caused by the complex elements can enhance the solubility of elements within the structure and promote the formation of a single-phase structure. The differences in electronegativity and ionic radii among the constituent elements introduce lattice distortion and sluggish-diffusion effect, playing a critical role in regulating the physical and chemical properties and micromorphology of HEMs. Due to these advantages, the high-entropy strategy has emerged as an effective approach for advancing the existing materials and developing novel ones. Thus, the diversity of HEMs has expanded from high-entropy alloys and intermetallic compounds to high-entropy oxides, sulfides, carbides, and so on. Consequently, their application fields are wide and show great potential in electrochemical energy storage fields.The development of high-performance solid-state electrolytes (SSEs) is essential for advancing solid-state batteries to satisfy the increasing demands for high energy density, enhanced safety, and long-term stability. As key components, SSEs play an indispensable role in providing migration pathways for alkali metal ions, making the facilitation of ion transport to achieve high ionic conductivity a primary objective in their development. Among various SSEs, inorganic ones have emerged as prominent candidates due to their relatively high ionic conductivity and stability. However, current inorganic SSEs require further improvements in ionic conductivity and overall performance to meet practical application requirements. A particularly important factor influencing the performance of inorganic SSEs is their local structural configuration. The arrangement of ions and the degree of structural order directly govern the migration energy barrier, which in turn has a great influence on ionic conductivity. Tailoring the local structure through compositional engineering and structural modulation offers a promising pathway to minimize migration energy barriers, thereby enhancing ion transport efficiency.Given the advantages of the high-entropy strategy in regulating local structures, this approach has been preliminarily applied to optimize the performance of inorganic SSEs, including oxide, sulfide, and halide SSEs. The mechanisms by which high-entropy strategies improve properties vary depending on the intrinsic characteristics of each prototype structure. For oxide SSEs, the incorporation of multiple elements effectively regulates site energy and refines the local structure of ion migration pathways, facilitating ion transport. In contrast, sulfide and halide SSEs benefit from their high anion tolerance, which enables the introduction of diverse anion species. This diversity disrupts the arrangement of adjacent Li⁺ and directly modulates ion migration behavior, contributing to improved ionic conductivity. This work systematically reviews the unique characteristics and performance enhancement mechanisms of high-entropy oxide, sulfide, and halide SSEs. Furthermore, it identifies key challenges and proposes future research directions aimed at advancing the design and improvement of high-entropy SSEs, paving the way for their application into next-generation solid-state batteries.Summary and prospectsThe high-entropy strategy is an effective approach for optimizing and developing SSEs. It can not only adjust the configurational entropy to stabilize the structure, but also enhance the ionic conductivity of SSEs by regulating site energy, structural disorder, and the distribution of mobile ions. For high-entropy oxide SSEs, cation substitution is primarily employed to regulate site energy and local structure, thereby improving ion transport properties. In high-entropy sulfide and halide SSEs, the anionic sublattice offers greater flexibility in composition. Hence, beyond cationic site regulation, modifications to the anionic sublattice result in a more pronounced effect on ionic conductivity. Furthermore, such strategies can regulate micromorphology, air stability, and resistance to oxidation and reduction, laying a solid foundation for high-energy-density and high-safety solid-state batteries.However, high-entropy solid-state electrolytes remain in their infancy, and their development faces several critical challenges and key issues. First, in the design of high-entropy solid-state electrolyte materials, the selection of elements critically governs the properties, while the compositional complexity poses significant challenges in establishing universal design principles. Besides, the development of high-entropy solid-state electrolyte materials necessitates careful trade-offs among different properties. A key scientific challenge lies in rationally choosing elements that simultaneously modulate structural configurations to enhance ionic conductivity while maintaining air stability and electrochemical stability. Current research has paid insufficient attention to elemental cost-effectiveness and safety implications, both of which substantially impact the practical application potential of these materials. Further investigations should prioritize the adoption of low-cost and high-safety raw materials to enhance the practical application. Second, current research on high-entropy SSEs mainly focused on the ionic transport properties. However, achieving practical applications requires a deeper investigation into their interfacial compatibility and stability with high-voltage cathodes and lithium metal anodes, which are critical for the performance of full battery systems. Third, future research could introduce machine learning methods to predict and screen elemental combinations and structural designs, thus accelerating the development of high-performance solid-state electrolytes. However, high-entropy solid-state electrolytes remain in the early exploratory stage, where limited experimental data and unclear structure-properties relationships constrain the accuracy of the data-driven model. To address this, researchers could combine conventional elemental doping strategies with quantitative analyses of individual element contributions to material performance. Concurrently, theoretical calculations could generate supplementary theoretical datasets. Furthermore, experimental validation should be employed to refine predictive models, establishing a “computation-data-experiment” collaborative framework. This approach will improve the model's reliability and generalizability, ultimately accelerating the rational design of high-entropy solid-state electrolytes.Although research on high-entropy SSEs is still in its early stages, these materials are expected to provide new avenues for advancing the practical applications of solid-state batteries through ongoing fundamental studies and technological innovations.