High-entropy alloys (HEAs) are advanced materials with unique compositions, typically consisting of five or more elements in nearly equal atomic ratios. Unlike traditional alloys, HEAs exhibit complex structures and properties, with high mixing entropy stabilizing fewer phases than predicted by traditional phase rules. This review explores the evolution of HEAs, focusing on their synthesis, stability, and crystallographic structures, as well as their mechanical properties and applications in extreme conditions. HEAs are classified into seven primary families based on their elements, with significant research on their potential in various fields. A major challenge in HEAs is the strength–ductility trade-off, which complicates their use as structural materials. Strategies such as TRIP and TWIP effects are employed to enhance mechanical properties without compromising ductility. Recent studies have identified promising single-phase HEAs, including FCC and BCC structures, with exceptional mechanical strengths. HEAs are also being explored for applications in hydrogen storage, energy conversion, catalysis, and magnetic applications. The unique atomic configurations in HEAs lead to diverse nearest-neighbor environments and a highly distorted energy landscape, contributing to their unique properties. The crystallographic structures of HEAs, such as FCC, BCC, and HCP, significantly influence their mechanical and physical properties. Research has shown that HEAs can exhibit phase transformations, such as martensitic transformation, which affect their mechanical behavior. The development of new HEA compositions, such as those with low-stacking-fault energy, has enhanced their performance in high-temperature and high-stress applications. The future of HEAs lies in their potential for advanced materials with tailored properties, driven by computational modeling, experimental validation, and innovative alloy design strategies. Challenges remain in scaling up HEA production and reducing costs, requiring collaboration between academia and industry. Overall, HEAs represent a promising direction in materials science, with potential applications in aerospace, nuclear, and other high-performance industries.High-entropy alloys (HEAs) are advanced materials with unique compositions, typically consisting of five or more elements in nearly equal atomic ratios. Unlike traditional alloys, HEAs exhibit complex structures and properties, with high mixing entropy stabilizing fewer phases than predicted by traditional phase rules. This review explores the evolution of HEAs, focusing on their synthesis, stability, and crystallographic structures, as well as their mechanical properties and applications in extreme conditions. HEAs are classified into seven primary families based on their elements, with significant research on their potential in various fields. A major challenge in HEAs is the strength–ductility trade-off, which complicates their use as structural materials. Strategies such as TRIP and TWIP effects are employed to enhance mechanical properties without compromising ductility. Recent studies have identified promising single-phase HEAs, including FCC and BCC structures, with exceptional mechanical strengths. HEAs are also being explored for applications in hydrogen storage, energy conversion, catalysis, and magnetic applications. The unique atomic configurations in HEAs lead to diverse nearest-neighbor environments and a highly distorted energy landscape, contributing to their unique properties. The crystallographic structures of HEAs, such as FCC, BCC, and HCP, significantly influence their mechanical and physical properties. Research has shown that HEAs can exhibit phase transformations, such as martensitic transformation, which affect their mechanical behavior. The development of new HEA compositions, such as those with low-stacking-fault energy, has enhanced their performance in high-temperature and high-stress applications. The future of HEAs lies in their potential for advanced materials with tailored properties, driven by computational modeling, experimental validation, and innovative alloy design strategies. Challenges remain in scaling up HEA production and reducing costs, requiring collaboration between academia and industry. Overall, HEAs represent a promising direction in materials science, with potential applications in aerospace, nuclear, and other high-performance industries.