The paper provides a comprehensive overview of ovonic threshold switch (OTS) materials and devices, highlighting their development history, key milestones, and recent advancements. OTS materials, primarily composed of chalcogenides, have gained significant attention due to their potential in 3D memory applications. The paper discusses the electrical parameters of OTS devices, including on-state current, off-state leakage current, selectivity, endurance, thermal stability, and switching speed. It also reviews the switching mechanisms of OTS devices, such as field-induced nucleation and carrier injection models. The paper categorizes OTS materials into Se-based, Te-based, and S-based systems, detailing their properties and performance. Se-based OTS materials, such as Ge-Se alloys, exhibit high crystallization temperatures, large mobility gaps, and low leakage currents. Te-based OTS materials, including Ge-Te alloys, show fast switching speeds but have lower thermal stability. S-based OTS materials, like Ge-S alloys, offer high drive current, low leakage current, and excellent scalability. Recent progress in OTS devices for 3D memory, self-selecting memory, and neuromorphic computing is also discussed. The paper highlights the successful application of OTS devices in 3D high-density memory and their promising performance and prospects in emerging applications. The development of OTS materials is driven by the need to optimize specific components, enhance thermal stability, reduce leakage current, and improve endurance. Doping processes and compositional optimization are crucial for improving material performance. Overall, the paper emphasizes the importance of OTS materials in advancing memory technologies, particularly in addressing the challenges of data storage in the era of big data and AIoT.The paper provides a comprehensive overview of ovonic threshold switch (OTS) materials and devices, highlighting their development history, key milestones, and recent advancements. OTS materials, primarily composed of chalcogenides, have gained significant attention due to their potential in 3D memory applications. The paper discusses the electrical parameters of OTS devices, including on-state current, off-state leakage current, selectivity, endurance, thermal stability, and switching speed. It also reviews the switching mechanisms of OTS devices, such as field-induced nucleation and carrier injection models. The paper categorizes OTS materials into Se-based, Te-based, and S-based systems, detailing their properties and performance. Se-based OTS materials, such as Ge-Se alloys, exhibit high crystallization temperatures, large mobility gaps, and low leakage currents. Te-based OTS materials, including Ge-Te alloys, show fast switching speeds but have lower thermal stability. S-based OTS materials, like Ge-S alloys, offer high drive current, low leakage current, and excellent scalability. Recent progress in OTS devices for 3D memory, self-selecting memory, and neuromorphic computing is also discussed. The paper highlights the successful application of OTS devices in 3D high-density memory and their promising performance and prospects in emerging applications. The development of OTS materials is driven by the need to optimize specific components, enhance thermal stability, reduce leakage current, and improve endurance. Doping processes and compositional optimization are crucial for improving material performance. Overall, the paper emphasizes the importance of OTS materials in advancing memory technologies, particularly in addressing the challenges of data storage in the era of big data and AIoT.