Retention and stability in orthodontic treatment are of critical importance for maintaining the achieved esthetic, functional, and occlusal outcomes. However, relapse remains one of the most significant clinical challenges due to the tendency of teeth and surrounding tissues to return to their initial positions. This review discusses the biological basis, risk factors, preventive strategies, and the effectiveness of retention appliances in maintaining post-treatment stability. Factors such as periodontal adaptation, quality of occlusal finishing, mandibular incisor dimensions, neuromuscular balance, and continued growth are key determinants of long-term stability. Approaches including overcorrection, interproximal reduction, supracrestal fiberotomy and frenectomy are highlighted as methods to enhance retention success. Supportive biophysical modalities, such as low-level laser therapy, mechanical vibration, and low-intensity ultrasound, may accelerate periodontal and skeletal adaptation; however, further clinical evidence is needed. Both removable and fixed appliances remain essential in retention therapy, with appliance selection determined by malocclusion type, patient compliance, and clinical requirements. Modern CAD/CAM-fabricated customized retainers also provide alternatives to conventional methods. Nevertheless, appliance breakage, hygiene challenges and relapse risk remain persistent concerns. Recent evidence emphasizes that retention should be planned from the outset of treatment, with individualized protocols and regular follow-up appointments. In conclusion, a lifelong retention approach is increasingly recognized as fundamental for the sustainability of orthodontic treatment success.