Subtalar instability is a complex clinical entity that is often associated with lateral ankle sprains and chronic ankle instability. This condition remains challenging to diagnose due to its similarity to lateral ankle instability and frequent coexistence in approximately 10–15% of cases. Key anatomical contributors to subtalar stability include the interosseous talocalcaneal ligament (ITCL) and calcaneofibular ligament (CFL). Diagnosis combines clinical history, physical examination, and imaging techniques, though distinguishing subtalar instability from related conditions remains difficult. Initial management involves conservative strategies, emphasizing rehabilitation to strengthen stabilizing structures. Surgical options are considered when nonoperative treatment fails, ranging from anatomical repair to nonanatomical reconstruction techniques. Despite advancements in imaging and surgical techniques, further improvements are needed to refine diagnostic criteria and treatment protocols. This review synthesizes the anatomy, biomechanics, diagnosis, and management strategies for subtalar instability, offering insights into its ongoing challenges and advancements.