Orthodontic treatment aims to achieve optimal dental alignment, functional occlusion, facial aesthetics, and long-term oral health. However, maintaining treatment results over time remains one of the greatest challenges in orthodontics. Despite advances in biomechanics, retention strategies, and treatment planning, post-treatment relapse continues to occur in varying degrees. Long-term stability is influenced by multiple biological, mechanical, growth-related, and behavioral factors. This review evaluates current evidence regarding the long-term stability of orthodontic treatment outcomes, examining factors contributing to relapse, retention protocols, treatment modalities, and technological advancements. The article discusses stability following extraction and non-extraction therapies, skeletal corrections, expansion procedures, and orthognathic surgery. Evidence suggests that while perfect stability is rarely achievable, long-term retention, individualized treatment planning, and continuous monitoring significantly improve treatment maintenance and patient satisfaction.