Background: The maxillary labial frenum (MLF) is a soft tissue fold connecting the upper lip to the alveolar process. Abnormal attachment can cause periodontal, functional, and esthetic problems. Differential diagnosis is important and can prevent unnecessary interventions. This study aims to summarize the current evidence on the assessment and management of abnormal MLF. Methods: A thorough review of the literature was conducted. Five online databases were searched for relevant peer-reviewed human studies. Article screening and data extraction were performed independently by two reviewers using predefined inclusion/exclusion criteria. Information about article type, study design, participants’ characteristics, interventions, and outcomes was extracted and synthesized. Results: 52 articles met the review criteria. MLF is a dynamic structure characterized by a wide normal morphological variation. MLF assessment in infants has not been standardized. Studies in pre-adolescents reported a change in the thickness and position of the MLF observed over time, resulting in a lower prevalence of abnormal MLF morphology. Studies in adolescents and adults reported variable differential diagnosis criteria. Lasers appear as the most advantageous frenectomy modality. Conclusions: There is a need for more objective MLF diagnostic protocols and treatment guidelines, which could prevent unnecessary surgical interventions.