Solid-state batteries (SSBs) may offer superior energy density, faster charging kinetics, better safety, and extended lifespan compared to conventional lithium-ion batteries that utilize flammable liquid electrolytes. These advantages position SSBs as a leading candidate for next-generation energy storage technologies, particularly in applications requiring high efficiency and safety, such as electric vehicles and renewable energy systems. At the core of SSB technology is the anode active material (AAM), which plays a crucial role in determining the battery’s energy density, cycling stability, and overall safety. This review systematically summarizes various AAMs employed in solid-state environments, encompassing a diverse range of materials, including metal-, carbon-, and alloy-based systems. Furthermore, it examines recent advancements in AAM design, focusing on innovative optimization strategies that enhance battery performance. By providing a thorough analysis of these materials and the progress made in their development, this review offers valuable insights into the future trends, opportunities, and challenges in the field of high-performance SSBs.